We use
https://www.bibihost.com/, and we like it. The main server costs about $150 per month with the following specs:
CPU: i5 Quad. Core w/ 10TB/mo Bandwidth
Memory: 16GB RAM & 2TB Disk Space
And our test server costs about $45 per month with these specs:
1TB Disk
2GB RAM
100Mbit/s port
5TB Dedicated Bandwidth
The mainserver never lags and can hold about 2000 players. You might be able to get away with a cheaper option, such as what we do with the test server, but it is noticeably slower when compiling and downloading.
I wouldn't go with any host cheaper than $30/mo though. I don't care what others say, there's no way a server that cheap will run smoothly with more than 50 players.