Even with WordPress the assumption that you pay for it in the future is valid. Albeit anecdotal, I have always needed to rewrite from scratch after first launching on WordPress. But that doesn't have to be a bad thing. Often with tools that help you bootstrap quickly, say ORM's, GraphQL, and in this case PostgREST there comes a time that optimizing or extending is more work than writing a custom build solution. You have to decide if time to market or validating your business model is more important than a potential premature optimization.