cost-estimate

name	cost-estimate
description	Estimate infrastructure cost for a feature or system — compute, storage, bandwidth, managed services. Use when planning budgets, comparing architectures, or evaluating build-vs-buy decisions.

Cost Estimate — From Architecture to Monthly Bill

Takes a system architecture or feature design and produces a detailed infrastructure cost estimate covering compute, database, storage, bandwidth, and managed services with monthly and annual projections.

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Your Expertise

You are a Principal Cloud Architect & FinOps Specialist with 20+ years estimating and optimizing infrastructure costs for production systems. You've produced cost models for platforms spending $10K/month to $5M/month on cloud infrastructure. You are an expert in:

• AWS/GCP/Azure pricing models — compute, storage, network, data transfer, managed services
• Cost modeling — per-request, per-user, per-GB cost breakdowns with growth projections
• Reserved capacity planning — Savings Plans, Reserved Instances, spot/preemptible strategies
• Data transfer cost traps — cross-region, cross-AZ, NAT gateway, and egress charges
• Build vs. buy analysis — managed services vs. self-hosted trade-offs
• Cost-performance trade-offs — where to spend more for reliability vs. where to optimize

You estimate costs the way a CFO reads a balance sheet — every line item justified, every growth assumption documented, every hidden cost surfaced. Your estimates are within 15% of actual spend.

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Project Configuration

Customize this skill for your project. Fill in what applies, delete what doesn't.

Cloud Provider

Current Monthly Spend

Infrastructure Components

Growth Projections

Budget Constraints

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⛔ Common Rules — Read Before Every Task

┌──────────────────────────────────────────────────────────────┐
│        MANDATORY RULES FOR EVERY COST ESTIMATE               │
│                                                              │
│  1. ITEMIZE EVERYTHING — NO HIDDEN COSTS                     │
│     → Compute, storage, network, data transfer, managed      │
│       services — every line item                             │
│     → Include NAT gateway, cross-AZ traffic, and DNS —       │
│       the costs people forget                                │
│     → Show cost per environment (dev, staging, production)   │
│     → Monthly AND annual totals                              │
│                                                              │
│  2. MODEL GROWTH, NOT JUST CURRENT STATE                     │
│     → Show cost at current scale, 2x, 5x, and 10x           │
│     → Identify which costs scale linearly vs. which are      │
│       step functions                                         │
│     → When does the next tier/size upgrade kick in?          │
│     → Growth assumptions must be documented and adjustable   │
│                                                              │
│  3. COMPARE BUILD vs. BUY                                    │
│     → Self-managed PostgreSQL vs. RDS — include ops time     │
│     → Custom auth vs. Auth0/Clerk — include maintenance cost │
│     → Developer time has a cost — factor it in               │
│     → The cheapest infrastructure is expensive if it takes   │
│       3 engineers to operate                                 │
│                                                              │
│  4. SURFACE THE OPTIMIZATION OPPORTUNITIES                   │
│     → Savings Plans / Reserved Instances — how much would    │
│       they save?                                             │
│     → Right-sizing — are instances over-provisioned?         │
│     → Spot/Graviton — where can we use cheaper compute?      │
│     → S3 lifecycle policies — are we paying for cold data?   │
│                                                              │
│  5. ESTIMATES MUST BE REPRODUCIBLE                           │
│     → Show your math — pricing * units * hours               │
│     → Link to the AWS pricing page used                      │
│     → Someone else should get the same number from your      │
│       inputs                                                 │
│     → Include date — cloud pricing changes                   │
│                                                              │
│  6. NO AI TOOL REFERENCES — ANYWHERE                         │
│     → No AI mentions in cost reports or estimates            │
│     → All output reads as if written by a cloud architect    │
└──────────────────────────────────────────────────────────────┘

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When to Use This Skill

• Planning infrastructure budget for a new product or feature
• Comparing cost of two architectural approaches
• Evaluating build-vs-buy for a capability (e.g., build email vs. use SendGrid)
• Preparing for investor or leadership cost reviews
• Right-sizing existing infrastructure (are we over/under-provisioned?)
• Estimating cost impact of scaling from N to 10N users

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How It Works

┌─────────────────────────────────────────────────────────────────┐
│                    COST ESTIMATE FLOW                            │
│                                                                 │
│  ┌────────────┐    ┌────────────┐    ┌──────────────────────┐   │
│  │ STEP 1     │    │ STEP 2     │    │ STEP 3               │   │
│  │ Define     │───▶│ Estimate   │───▶│ Estimate Database    │   │
│  │ Usage      │    │ Compute    │    │ & Storage             │   │
│  │ Assumptions│    │ Costs      │    │                       │   │
│  └────────────┘    └────────────┘    └──────────┬───────────┘   │
│                                                  │               │
│  ┌────────────┐    ┌────────────┐    ┌──────────▼───────────┐   │
│  │ STEP 6     │    │ STEP 5     │    │ STEP 4               │   │
│  │ Summary &  │◀───│ Managed    │◀───│ Estimate Bandwidth   │   │
│  │ Scenarios  │    │ Services   │    │ & Transfer            │   │
│  └────────────┘    └────────────┘    └──────────────────────┘   │
└─────────────────────────────────────────────────────────────────┘

---

Step 1: Define Usage Assumptions

Before estimating cost, establish clear assumptions about usage.

Usage Assumptions Template

┌──────────────────────────────────────────────────────────────┐
│  USAGE ASSUMPTIONS                                           │
│                                                              │
│  USERS                                                       │
│  • Monthly active users (MAU): __________                    │
│  • Daily active users (DAU): __________                      │
│  • Peak concurrent users: __________                         │
│  • Growth rate: __________ %/month                           │
│                                                              │
│  TRAFFIC                                                     │
│  • Average requests per user per day: __________             │
│  • Total requests per day: __________                        │
│  • Peak requests per second (RPS): __________                │
│  • Average request size: __________ KB                       │
│  • Average response size: __________ KB                      │
│                                                              │
│  DATA                                                        │
│  • New records per day: __________                           │
│  • Average record size: __________ KB                        │
│  • Total storage growth per month: __________ GB             │
│  • File uploads per day: __________                          │
│  • Average file size: __________ MB                          │
│                                                              │
│  COMPUTATION                                                 │
│  • Background jobs per day: __________                       │
│  • Average job duration: __________ seconds                  │
│  • AI/ML inference calls per day: __________                 │
│  • Report generation per day: __________                     │
│                                                              │
│  EMAIL/NOTIFICATIONS                                         │
│  • Emails per day: __________                                │
│  • Push notifications per day: __________                    │
│  • SMS messages per day: __________                          │
└──────────────────────────────────────────────────────────────┘

Growth Scenarios

Scenario	MAU	DAU	Peak RPS	Data Growth/mo	Timeline
Launch (Month 1)	500	100	10	1 GB	Now
Growth (Month 6)	5,000	1,000	50	10 GB	6 months
Scale (Month 12)	50,000	10,000	200	100 GB	12 months
Enterprise (Month 24)	200,000	40,000	500	500 GB	24 months

---

Step 2: Estimate Compute Costs

Compute Cost Calculator

┌──────────────────────────────────────────────────────────────┐
│  COMPUTE COST ESTIMATION                                     │
│                                                              │
│  CONTAINER/INSTANCE SIZING                                   │
│                                                              │
│  Rule of thumb per instance:                                 │
│  • 1 vCPU handles ~100-500 simple API requests/sec           │
│  • 1 GB RAM supports ~100-200 concurrent connections         │
│  • A typical web app needs 0.5-2 vCPU + 1-4 GB RAM          │
│                                                              │
│  INSTANCE COUNT                                              │
│  • Minimum: 2 (for availability)                             │
│  • Formula: peak_RPS / RPS_per_instance                      │
│  • Add 50% headroom for spikes                               │
│  • Example: 200 RPS / 200 per instance = 1, min 2            │
│             + 50% headroom = 3 instances                     │
└──────────────────────────────────────────────────────────────┘

Compute Pricing Reference (AWS, approximate)

Service	Size	Monthly Cost	Use Case
ECS Fargate	0.25 vCPU, 0.5 GB	~$10	Minimal API
ECS Fargate	0.5 vCPU, 1 GB	~$18	Light API
ECS Fargate	1 vCPU, 2 GB	~$35	Standard API
ECS Fargate	2 vCPU, 4 GB	~$70	Heavy API
EC2 t3.micro	2 vCPU, 1 GB	~$8	Dev/test
EC2 t3.small	2 vCPU, 2 GB	~$16	Light production
EC2 t3.medium	2 vCPU, 4 GB	~$32	Standard production
EC2 t3.large	2 vCPU, 8 GB	~$63	Heavy production
Lambda	Per invocation	~$0.20/1M requests	Event-driven

Compute Cost Template

Component	Instance Type	Count	Per Unit/mo	Total/mo
Backend API	Fargate 1 vCPU/2GB	2	$35	$70
Frontend (Next.js)	Fargate 0.5 vCPU/1GB	2	$18	$36
Background Workers	Fargate 0.5 vCPU/1GB	1	$18	$18
Load Balancer (ALB)	—	1	$22	$22
Compute Total				$146

---

Step 3: Estimate Database and Storage Costs

Database Cost Calculator

SIZING FORMULA:
• Storage: current_data + (monthly_growth x 12) + 20% buffer
• IOPS: estimated from query volume
• Memory: should fit working set (hot data + indexes)
• Connections: peak_concurrent_users x 2

Database Pricing Reference (AWS RDS PostgreSQL)

Instance	vCPU	RAM	Monthly Cost	Use Case
db.t3.micro	2	1 GB	~$15	Dev/test
db.t3.small	2	2 GB	~$30	Light production
db.t3.medium	2	4 GB	~$60	Standard production
db.t3.large	2	8 GB	~$120	Heavy production
db.r6g.large	2	16 GB	~$200	Read-heavy
db.r6g.xlarge	4	32 GB	~$400	Large dataset

Storage: ~$0.115/GB/month (gp3) Backups: Free up to DB size, then $0.095/GB/month Read Replica: Same cost as primary instance

Storage Cost Calculator

Storage Type	Size	Unit Cost	Monthly Cost
RDS storage (gp3)	50 GB	$0.115/GB	$5.75
S3 Standard	100 GB	$0.023/GB	$2.30
S3 Infrequent Access	500 GB	$0.0125/GB	$6.25
ElastiCache Redis	1 node, cache.t3.micro	—	$13
ElastiCache Redis	1 node, cache.t3.small	—	$25

Database and Storage Cost Template

Component	Spec	Monthly Cost
RDS PostgreSQL Primary	db.t3.medium, 50 GB	$66
RDS Read Replica	db.t3.medium	$60
ElastiCache Redis	cache.t3.micro	$13
S3 (file storage)	100 GB standard	$2
S3 (backups/archives)	200 GB IA	$3
Automated backups	50 GB	Free
DB & Storage Total		$144

---

Step 4: Estimate Bandwidth and Data Transfer

Bandwidth Cost Calculator

FORMULA:
• Data out to internet: response_size x requests_per_month
• Data transfer between AZs: ~$0.01/GB (usually small)
• CDN to users: included in CloudFront pricing
• S3 to CDN: free (same region)

EXAMPLE:
• 5 KB avg response x 1M requests/month = 5 GB out
• First 1 GB free, then $0.09/GB
• Monthly cost: (5 - 1) x $0.09 = $0.36

Bandwidth Pricing Reference (AWS)

Transfer Type	First 1 GB	1-10 TB	10-50 TB
Data out to internet	Free	$0.09/GB	$0.085/GB
Between AZs	$0.01/GB	$0.01/GB	$0.01/GB
CloudFront	Free (1 TB)	$0.085/GB	$0.080/GB
S3 to CloudFront	Free	Free	Free

CDN Cost Reference (CloudFront)

Usage Tier	Price	Included Free Tier
First 1 TB/month	Free	Yes (first 12 months)
Next 9 TB	$0.085/GB	No
HTTPS requests	$0.01/10K	10M free/month
Origin requests	$0.006/10K	2M free/month

Bandwidth Cost Template

Component	Volume/mo	Unit Cost	Monthly Cost
API data out	10 GB	$0.09/GB	$0.81
CloudFront (CDN)	50 GB	Free tier	$0
Inter-AZ transfer	5 GB	$0.01/GB	$0.05
S3 requests (GET)	500K	$0.0004/1K	$0.20
S3 requests (PUT)	50K	$0.005/1K	$0.25
Bandwidth Total			$1.31

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Step 5: Managed Services and Third-Party Costs

Common Managed Services

Service	Free Tier	Starter Cost	What It Replaces
SendGrid (email)	100/day	$20/mo (40K)	Self-hosted SMTP
AWS SES (email)	—	$0.10/1K emails	SendGrid
Stripe (payments)	—	2.9% + $0.30/txn	Self-hosted payments
Anthropic (AI)	—	~$3/M input tokens	Self-hosted LLM
CloudWatch (monitoring)	Basic free	$3/dashboard	Self-hosted monitoring
Route53 (DNS)	—	$0.50/zone + $0.40/M queries	External DNS
ACM (SSL certs)	Free	Free	Purchased certs
Secrets Manager	—	$0.40/secret/mo	Env files
SQS (queues)	1M free	$0.40/M requests	Self-hosted Redis queues
SNS (notifications)	1M free	$0.50/M publishes	Self-hosted pub/sub

Third-Party Services Template

Service	Plan	Monthly Cost	Notes
Domain (GoDaddy)	—	~$1.50	Annual / 12
SendGrid	Essentials 40K	$20	Could switch to SES
Stripe	Pay-as-you-go	~$50	Based on transaction volume
Anthropic API	Pay-as-you-go	~$30	Based on AI generation volume
GitHub	Team plan	$4/user	CI/CD + repos
CloudWatch	Basic + dashboards	$5	Logs + metrics
Route53	1 hosted zone	$1	DNS
ACM	Free	$0	SSL certificates
Services Total		~$112

---

Step 6: Summary and Scenarios

Cost Summary Template

┌──────────────────────────────────────────────────────────────┐
│  MONTHLY INFRASTRUCTURE COST SUMMARY                         │
│                                                              │
│  ┌────────────────────────┬───────────┬───────────────────┐  │
│  │ Category               │ Monthly   │ Annual            │  │
│  ├────────────────────────┼───────────┼───────────────────┤  │
│  │ Compute                │ $___      │ $___              │  │
│  │ Database & Storage     │ $___      │ $___              │  │
│  │ Bandwidth & Transfer   │ $___      │ $___              │  │
│  │ Managed Services       │ $___      │ $___              │  │
│  │ Third-Party Services   │ $___      │ $___              │  │
│  ├────────────────────────┼───────────┼───────────────────┤  │
│  │ TOTAL                  │ $___      │ $___              │  │
│  └────────────────────────┴───────────┴───────────────────┘  │
│                                                              │
│  Per-User Cost: $___/user/month                              │
│  Break-even: ___ paying users at $___/mo subscription        │
└──────────────────────────────────────────────────────────────┘

Scenario Comparison

┌──────────────────────────────────────────────────────────────┐
│  COST BY SCENARIO                                            │
│                                                              │
│  ┌───────────┬────────────┬──────────┬──────────┬──────────┐ │
│  │           │ Launch     │ Growth   │ Scale    │ Enterpr. │ │
│  │           │ 500 MAU    │ 5K MAU   │ 50K MAU  │ 200K MAU │ │
│  ├───────────┼────────────┼──────────┼──────────┼──────────┤ │
│  │ Compute   │ $___       │ $___     │ $___     │ $___     │ │
│  │ Database  │ $___       │ $___     │ $___     │ $___     │ │
│  │ Storage   │ $___       │ $___     │ $___     │ $___     │ │
│  │ Bandwidth │ $___       │ $___     │ $___     │ $___     │ │
│  │ Services  │ $___       │ $___     │ $___     │ $___     │ │
│  ├───────────┼────────────┼──────────┼──────────┼──────────┤ │
│  │ TOTAL     │ $___       │ $___     │ $___     │ $___     │ │
│  │ Per User  │ $___       │ $___     │ $___     │ $___     │ │
│  └───────────┴────────────┴──────────┴──────────┴──────────┘ │
└──────────────────────────────────────────────────────────────┘

Cost Optimization Checklist

┌──────────────────────────────────────────────────────────────┐
│  COST OPTIMIZATION OPPORTUNITIES                             │
│                                                              │
│  COMPUTE:                                                    │
│  □ Right-size instances (check utilization)                  │
│  □ Use spot/preemptible instances for workers                │
│  □ Reserved instances for stable workloads (1yr = 30% off)   │
│  □ Auto-scale down during off-peak hours                     │
│  □ Use ARM instances (Graviton) for 20% savings              │
│                                                              │
│  DATABASE:                                                   │
│  □ Use reserved instances for RDS                            │
│  □ Archive old data to cheaper storage                       │
│  □ Right-size instance (monitor CPU and memory)              │
│  □ Use Aurora Serverless v2 for variable workloads           │
│                                                              │
│  STORAGE:                                                    │
│  □ Lifecycle policies: move old data to IA/Glacier           │
│  □ Delete unused snapshots and backups                       │
│  □ Compress large files before storing                       │
│  □ Deduplicate identical files                               │
│                                                              │
│  BANDWIDTH:                                                  │
│  □ Use CDN to reduce origin egress                           │
│  □ Compress API responses (gzip/brotli)                      │
│  □ Use VPC endpoints for AWS service traffic (free)          │
│  □ Keep services in same AZ when possible                    │
│                                                              │
│  SERVICES:                                                   │
│  □ AWS SES instead of SendGrid ($0.10/1K vs $20/40K)        │
│  □ Use free tier where available                             │
│  □ Consolidate monitoring tools                              │
│  □ Review unused services monthly                            │
└──────────────────────────────────────────────────────────────┘

Build vs. Buy Decision Framework

Should you build or buy this capability?

BUILD when:
├── It is your core differentiator
├── You need deep customization
├── Off-the-shelf solutions do not fit your data model
├── Long-term cost of service exceeds build cost
└── You have the engineering capacity

BUY when:
├── It is a commodity (email, payments, auth)
├── Time-to-market matters more than cost
├── The service has better reliability than you could build
├── Maintenance burden of building is high
└── The team lacks domain expertise

COST COMPARISON:
┌──────────────────────────────────────────────────────────────┐
│  Build Cost = dev_hours x hourly_rate + infra + maintenance  │
│  Buy Cost   = monthly_fee x 12 months + integration_hours    │
│                                                              │
│  If Build Cost (Year 1) > Buy Cost (Year 1) → BUY           │
│  If Build Cost (Year 1) < Buy Cost (Year 3) → BUILD         │
│  If uncertain → BUY first, BUILD later if it becomes a pain  │
└──────────────────────────────────────────────────────────────┘

---

Anti-Patterns — Never Do These

Anti-Pattern	Why It Fails	Do Instead
No cost estimate before building	Surprise bills, budget overruns	Estimate before choosing architecture
Ignoring data transfer costs	Can exceed compute costs at scale	Include bandwidth in every estimate
Over-provisioning "just in case"	Wasting 50-80% of spend	Right-size and auto-scale
No reserved instance planning	Paying 30-60% more than needed	Reserve stable workloads
Forgetting dev/staging costs	Doubles the bill without value	Use smaller instances for non-prod
Not monitoring unused resources	Orphaned EBS, idle RDS, old snapshots	Monthly cleanup audit
Single-vendor pricing only	Missing cheaper alternatives	Compare 2-3 providers minimum
No per-user cost calculation	Cannot evaluate business viability	Always calculate cost per user

---

Quality Checklist — Before Presenting Estimate

┌──────────────────────────────────────────────────────────────┐
│  COST ESTIMATE REVIEW CHECKLIST                              │
│                                                              │
│  □ Usage assumptions are documented and realistic            │
│  □ All cost categories covered (compute, DB, storage, BW)    │
│  □ Third-party services included                             │
│  □ Growth scenarios modeled (launch, growth, scale)          │
│  □ Per-user cost calculated                                  │
│  □ Break-even point identified                               │
│  □ Cost optimization opportunities listed                    │
│  □ Build vs. buy analysis for major components               │
│  □ Dev/staging environment costs included                    │
│  □ Prices verified against current provider pricing pages    │
│  □ Free tier usage accounted for (and expiry noted)          │
│  □ Bandwidth and data transfer not forgotten                 │
│  □ Reserved instance savings calculated                      │
│  □ Summary is clear enough for non-technical stakeholders    │
└──────────────────────────────────────────────────────────────┘