What type of sound quality are you looking for? Is this just for your own entertainment, or a demo to try to get gigs or a self published CD? Hell you could put one $20 radio shack mic in the room and hope for the best if you just want to get sound onto "tape". But for a decent home studio sound I would suggest a pair of small diaphragm condensor mics for overheads. A sm57 on the snare and a mic with good low end response in the kick. Check the microphone forum for discussions of mics and prices but a basic set up could look like this:
pair MXL 603s $199
Shure sm57 $ 79
Shure Beta 52 $180
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$458 oh and don't forget cables and mic stands, about another $80 and make sure the drummer changes his heads, he should pay for that so you don't have to (unless you're providing the kit, then it's up to you to have fresh heads and properly tune them)