I use Firebase Realtime Database, and the price is coming from the outgoing traffic. I used to pay a couple of dollars for that, but for the last year, the number grew from 20 to 50 (this month it's 60). It definitely could be optimized, but it will cost me dozens of hours which would be much more expensive than hosting. Also, I have more important things to do for the library.
What do you use the database for? Looking at your site, i see nothing that looks not like a normal static site
For storing documentation for every version of date-fns. You can see the source code: github.com/date-fns/date-fns.org
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