If you need to soundproof, egg carton sheets do the job cheaply. How you plan on recording will play into things too. Live recording, you may want to have a decent amount of space so sounds won't bleed over, depending on mic quality. Track by track, you don't have to worry about it all that much.
If you've got a laptop that will run it, which a lot of sound programs can be VERY taxing on sound cards and processors, you can just pick up a decent... $50? dollar mixer with enough inputs to suit your needs.
For the longest time, and this was almost 8 years ago now, me and my buddies had a setup of
Drums at back wall, guitar cab in one corner, bass cab in the other, and vocal mic center front. We had some old digital 8 track recorder, condenser mics on each cab, vocal mic running in too, obviously, and our drummer used the remaining inputs for his shit, fuck trying to even think about how we mic'd drums in some cheap rigged way, I hate drum micing. Condenser mics were probably $80 each, but a solid investment, 8 track our bassist had, but was $100 I think.
Worked fine for live recording practices and was pretty good quality.
If you've got a decent computer and some cash,
We had a friend back in the day that let us abuse the hell out of his. Ran it through cakewalk, and it was beautiful.