That leaves out staffing, backups, development and testing of a multi-location failover mechanism as robust as the RDS one, and a bunch of security compliance work if that’s relevant.
It’s totally possible to beat AWS and volume is the way to do it–your admin’s salary doesn’t scale be linearly with storage–but every time I’ve tried to account for all of the costs it’s been close enough that it’s made sense to put people on things which can’t be outsourced.
If this database is a large portion of the infrastructure required then the fixed-ish costs don't scale so well, but a smaller cloud/hosting company should be considered.
But I have over 60 servers. Using the pricing calculator for the two AWS SaaS services that closely align with our primary service (40+ of those servers), we'd face a cost of over $1.2M/year if reserved for 3 years and paid upfront — that's for the service alone, I haven't added any bandwidth costs, or getting the data into those systems, and I've picked the minimum values for storage and throughput as I don't know what these should be. (Probably not the minimum.)
Add the remaining compute (~20 decent servers), a petabyte-scale storage pool, and all the rest, and the bill would likely exceed our entire IT budget including hardware, hosting, cloud services we do use, and all the salaries.
My rough estimate is our infrastructure costs would increase 8-10 times using AWS, our staff costs wouldn't reduce, and the risk to the budget would increase with variable usage.
This is tax money being spent, so I am asked every few years to justify why we aren't using cloud. (That's why I'm putting this much effort into a HN reply, the question was asked again recently.)
I know someone working in another country on essentially the same system for that country. They went all-in on AWS and pay every 1-2 months what we spend in a year, but have a fraction of our population/data.
It’s totally possible to beat AWS and volume is the way to do it–your admin’s salary doesn’t scale be linearly with storage–but every time I’ve tried to account for all of the costs it’s been close enough that it’s made sense to put people on things which can’t be outsourced.