Plenty of decent condenser mics around $100 out there. That's one thing I'd get.
Some sort of preamp/computer interface-again, a lot of options out there, as Woodman points out, a lot depends on what kind of computer rig you have right now. Lots of times, there will be bundled software as well-just check to make sure your machine is up to the task of running it.
You might already have a bunch of the other things you need already at hand-decent mic and instrument cables, sound processing gear (reverbs, compressors, and the like) and some decent dynamic mics like a Shure SM-57 (I always have 2 of them handy!).
What else you need depends on how adventurous you want to get...
Franc Robert