My approach is to use managed DB instance and to share it between projects: create dbs inside the same instance. In this way the cost of instance is split between all the projects. Also this service is on my todo list to try for this use case https://neon.tech

I self host and optimize my own instance of DB engines. I’ve got one for Maria, Postgres, mongo, etc. put multiple DBs with dedicated users and permissions. Obviously if you have certain data requirements you might need a dedicated instance and not sure between projects, but I run everything myself.

I personally use CockroachDB hosted on Cockroach Cloud, it’s not Postgres but it’s compatible with most tools in the Pg ecosystem and their Cloud offering is very nice. I migrated a few months ago and it was fairly smooth bar a few changes in my Go code and a few types in the schema.

I use @supabasecom

As an alternative to Postgres I’ve started to use Cloudflare D1 (sqlite) more and more (often in combo with CF Workers (functions), Queues and R2 (S3-like storage)).

15$ per month in digita ocean

On my VPS beside my app, both via docker compose

I think for the one project I have with a db I deployed it with digital ocean and then use a gcp bucket. I think i pay maybe $6 a month right now?? But it's also incredibly small.