Just out of curiousity but what did you get out of it? I mean if they get to pick it, get the responsibility of AWS on you, but do you also get to get paid those money after saving them money? I mean the way I see it, is that 16k/month don't only pay for the hardware, but also to keep headaches away and to have someone to blame
IIRC I got to move some heavy analytics queries, which could not be ran on a read only replica (rollups) and without hearing the word budget once. Main db remained on RDS.
