I can't talk about staff costs, but as someone who's self-hosted Postgres before, using RDS or Supabase saves weeks of time on upgrades, replicas, tuning, and backups (yeah, you still need independent backups, but PITRs make life easier). Databases and file storage are probably the most useful cloud functionality for small teams.

If you have the luxury of spending half a million per year on infrastructure engineers then you can of course do better, but this is by no means universal or cost-effective.