DB guy to tune the instance the database runs on + figure out your streaming backups etc. It's not a full time job, but it's a couple of days a week; and completely taken care of if you use RDS

I think your estimate is off by a factor of about 40. RDS is great at what it does, but it doesn't do that much. Getting the stuff RDS gives you for "free" might take a a few days to set up, but after that, your automated backups are going to take just as much of your time as the ones RDS gives you, ie, none.

If RDS saves you 30 minutes a week I'd be surprised.

A couple of days a week? That's ridiculous, once you have established procedures the only thing left is regular OS maintenance tasks which are the same as the rest of your servers.

Indeed. RDS saves like 1 day setup. No ongoing difference.