> Right now, we have about 800 monthly donors and about $7,500 in monthly donations. That covers our server costs pretty much exactly.
For only 2M registered (not even monthly) users? Tell me you are using AWS without telling me you are using AWS.
Let's think about their heaviest workload, which is likely running user-submitted code server-side to test those exercise submissions. Say it's really bad performance-wise and costs 1s of single-core CPU time per submission. 45m submission gets us 520 days of CPU time.
I'm going to go out on a limb and claim their entire site could run off a $50/month dedicated server, and it would be unimpressed.