Add up the layers every live product has: the AI tool you build with, hosting, a database, email, a domain, monitoring, model usage and payment fees. On the book's default stack the fixed part is about $74 a month plus the domain, as listed in October 2026; the fees then scale with every sale. Put the layers in one sheet so you see the number instead of feeling it.
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Pick your tools, overwrite any price with what the provider's page says today, set your price and expected sales. Defaults are prices as listed in October 2026 and are there to be checked. Free, no sign-up, nothing leaves your browser.
| Layer | Book's default | Monthly (as listed, Oct 2026) | Note |
|---|---|---|---|
| AI build tool | Claude Pro | $20 | Includes Claude Code; shares the plan's usage limits |
| Hosting | Vercel Pro | $20 | Includes $20 usage credit; Hobby is non-commercial |
| Database and auth | Supabase Pro | $25 | 8 GB, never paused |
| Resend Free | $0 | 3,000 a month, 100 a day; Pro is $20 for 50,000 | |
| Code | GitHub Free | $0 | Private repos included |
| Domain | Your registrar | Your figure | Yearly fee divided by 12 |
| Error monitoring | Free tier of your tool | $0 | Check its limits |
| Model usage | Sonnet 5.5 summaries | $9 | 1,000 calls at $0.009 |
| Fixed total | $74 + domain |
The book's worked example (Part 18): a client-approval portal with 20 agencies at £29 each. Stripe's UK standard-card fee of 1.5% + 20p makes each payment cost £0.635, so 20 payments cost £12.70; if half the cards were international at 3.15% + 20p the month's fees become £17.45. Break-even on fixed costs is fixed ÷ (price − fee per sale): £57 ÷ (£29 − £0.635) ≈ 2.01, so three subscribers.
Monthly fixed cost = tool + hosting + database + email + domain ÷ 12 + other + model usage. Model usage = requests × (input tokens × input price + output tokens × output price) ÷ 1,000,000, converted at your rate. Cost per sale = price × fee % + fixed fee. Break-even = fixed cost ÷ (price − cost per sale), rounded up. Monthly result = sales × (price − cost per sale) − fixed cost. The sheet excludes your time, which is the real cost, and taxes on what you earn.
Prices and limits are as listed by the providers in October 2026 and are reproduced from the book for education only; they change, so check each pricing page before you decide. Not financial, tax or legal advice. No result or income is promised.
This tool puts a few of the named techniques from Build Software With AI to work. Each line says how it relates to the tool.
See every technique in Build Software With AI →
Every live product has the same layers: the AI tool you build with, hosting, a database, email, code storage, a domain, monitoring, payment fees and, if you add AI features, model usage. On the default stack in the book (Claude Pro $20, Vercel Pro $20, Supabase Pro $25, Resend free, GitHub free) the fixed total is about $74 a month plus the domain and model usage, as listed in October 2026. Payment fees then scale with sales.
Vercel describes the Hobby plan as for personal, non-commercial use; it is capped and you cannot buy more usage. The book's upgrade trigger is before the first paid customer: Pro is $20 a month with $20 of included usage, as listed in October 2026. Check Vercel's current pricing page.
Not for anything customers rely on. The free tier is 500 MB per project, at most two active projects, and a project is paused after one week of inactivity. Pro is from $25 a month, 8 GB per project and never paused, as listed in October 2026.
You pay per token, separately for input and output. Multiply the tokens per request by the price per million tokens for each side and add them. As listed in October 2026, Claude prices run from $0.10 input and $0.50 output per million tokens (Haiku 5.5) to $10 input and $50 output (Fable 5.1), so the same feature can cost a hundred times more on a bigger model. Prompt caching can cut the input side further.
A processor such as Stripe moves the money and leaves you responsible for sales tax, VAT or GST and disputes; a merchant of record is legally the seller, collects and remits indirect taxes and handles chargebacks, for a higher fee. As listed in October 2026: Stripe standard UK cards 1.5% + 20p, Paddle and Lemon Squeezy 5% + 50 cents, Dodo Payments 4% + 40 cents on US domestic cards. Check each provider's current pricing page.
All prices and limits are as reproduced in Build Software With AI (Parts 3, 14, 15, 17 and 18) from the providers' pages in October 2026 and are there to be replaced with today's figures. Exchange rates are approximate defaults; enter today's rate.