Which works out at $100 USD / year. You might think that's trivial, but when you start provisioning multiple environments over multiple projects it starts to add up.
It's a shame that Google haven't managed to come up with a scale to zero option or serverless alternative that's compatible.
Sheet Ninja is 108 USD / year and has tiny capacities for every metric. SQLite is free and would stomp this in every aspect on low budget hosting. Even a tiny API that stores CSV would be magnitudes more efficient.
But what would scare me the most, is that google can easily shut this thing down.
setup a DB project , use same cloud sql instance for all DBs. Did that for years on non prod or experimental projects. $100 is a bargain for what you get in terms of resiliency
It is trivial to set up a database on GCP given that you know what you are doing and I would pay Google for that stability and support for setting up multi-tenancy and region.
Using Google spreadsheets as a backend will just cause them to charge everyone later.
Sheet Ninja isn't free. Even on their side, "free" does not mean what you think it means.