My postgres process doesn't come close to using up enough resources to push me out of even the cheap VPS tiers and I don't have to worry about locking if there's a heavy write load.
I think the point here is, SQLite setup would provide satisfactory results at this scale.
If the choice is betweeen a PAAS database offering and SQLite, you can pick SQLite. If you have skills / are prepared for managing dbserver yourself, then do that.