You're going to have to pay to host your Rails/Django/Whatever app anyway, and you're also going to have to pay for a hosted Postgres solution, so why not just

You're going to have to pay to host your Rails/Django/Whatever app anyway, and you're also going to have to pay for a hosted Postgres solution, so why not just get them both in one deal and then also dispense with the need for a bunch of Rails code thanks to the auth and REST api that is built in to Supabase.