Maybe the failure is in trying only one model / one prompt.
I'm also convinced the effect would not be there If I had a 10$ budget.
Sure it would be. I pay $10/month to OpenCode for a Go subscription, it's fine for day-to-day coding tasks. I wouldn't necessarily try and one-shot a production app on that budget, but with decent planning and test-driven-development, it gets the job done
Actually, I lied, Codex is free and I developed my first AI written application using it and the free tier limits were generous enough to work on it for several months.