It depends what level of quality you're going for.
If it's simple home recording, you can get away with using the compressor on a typical multi-effects guitar pedal. You don't want to use too much compression, just enough to even the sound out and let you get a hotter signal to tape.

If you're into more of a pro-level of recording, you'd be looking at about $2500 for an Avalon at the upper end.
There's lots of other makes in between obviously, it's just a matter of how smooth a sound you're going for.

Best bet is to try Googling some recording studios and checking their equipment list. It'll give you a good idea of what most people use.