What kind of specs do you need for the server? If your having 20 or so people join your server you also have to look at your upload/download internet speeds as well.
I have a HP DL380 gen6 that runs Hyper-v 4 core 16GB of ram for a Rust server and does just fine. theoretical i could spin up 3 maybe 4 VM servers for rust on 1 DL380 and could be fine.
Gen6 and 7 are really cheap on ebay, a gen 8 would push the budget maybe just depends on what deal you can find.