Debris is free, and stays free.
No ads, no purchases, no analytics, no accounts, and nothing in the app is behind a payment. If you feel like giving back, here are the ways, but the app is exactly the same either way.
github.com/sponsors/mews-se
One-off or monthly, and it shows up next to the code.
buymeacoffee.com/mstockkonsult
Card payment, no account needed.
Signing a Mac app with a Developer ID and having Apple notarize it, so that macOS opens it without a warning, requires the Apple Developer Program, 99 USD a year. Anything beyond that is a thank you, not a budget.