The two real costs, not the vague answer
"It depends" is technically true and useless. There are exactly two costs to account for: what the AI agent itself costs to use, and what it costs to host the thing once it's running. Everyone asking this question is really asking about both at once, so here's both, with real numbers pulled from the 173 apps on this register rather than a guess.
Across every app here, the average pay-per-token agent cost — if you don't already have a subscription — comes out to roughly $53–$104 for a single build. That's not a subscription fee, that's the one-time cost of the actual build session, scaled by how much work the specific app takes.
Most of the time, hosting is free
This is the number that surprises people: 82% of the apps on this register can be hosted for genuinely $0 a month at personal scale, using ordinary free tiers of real providers — not a trick, not a temporary promo, just what a small personal project actually costs on modern infrastructure. That's the honest answer for most build-it-yourself projects: the agent cost is real and one-time, the hosting cost is usually nothing.
The 18% where hosting isn't free follow a clear pattern, not a random distribution. Look at what's actually driving that cost and it's almost always one of a few specific things: real-time collaboration (a live cursor moving on someone else's screen), bank-account aggregation, or video infrastructure. Simple CRUD apps, content sites, and internal tools are essentially always free to run.
If you already have an agent subscription
The agent-cost number above assumes you're paying per API token with no subscription. If you already pay for an agent subscription — Claude Pro or Max, Cursor, or similar — the marginal cost of one more build is $0. It's already covered by a bill you're paying anyway. This is the actual reason 'building it yourself' so often nets out cheaper than a subscription you're trying to replace: you're not adding a new cost, you're using one you already have.
What this means for a real decision
The 173 apps on this register list for a combined $4,359 a month if you paid for every one of them — over $52,000 a year. Even the apps genuinely worth just paying for aren't worth $52,000 a year collectively; most people pay for a handful. But for the ones scoring well on buildability, the math is rarely close: a $53-104 one-time build cost against a subscription charging that same amount every single month isn't really a comparison, it's a rounding error against a year of payments.
The honest caveat: these are estimates for planning, not a bill forecast. Your actual cost depends on your agent, how many iterations it takes you, and which model you're using. See the method behind these numbers on the cost breakdown that appears on every app page.