I'm sure you have good reasons to rent a Dedicated Server, but you might want to think about whether or not your current connection (i.e., cable), and hardware, or even an extra (older) PC can do the trick in the meantime.
I run a Half-Life DS for a few friends (and sometimes open it up to the public) on the weekends. It runs on a Linux Mandrake 9.2 / P3-733 MHz platform with 384 MB. I can comfortably host 10-15 players with no problem with my cable connection. I have even run a BF1942 game, with 10 players. I haven't pushed my server for that game's capacity yet - considering it's fairly graphics intensive compared to HL.
If you're thinking beyond the hobby/dabbling realm, then there are some serious DS leasors out there, like
these guys, among others.