A lot of this is penny wise pound foolish. Managed services cost more, but they provide more. RDS is just such a simple slam dunk for what you get for the cost. How much does it cost to spend 8-20 hours a week handling maintenance and upgrades and scaling for these services? I guess I'm bitter working on a project that was built with all sorts of crazy custom deployment stuff too conserve costs that's a total OPs nightmare. Moving from Redis on EC2s to elasticache was such an upgrade. We constantly had little issues here and there.

Edit - Alsocontainerize your app from the start so that if it does take off you can slam it in ecs or k8s.