since you have a $600 budget try these.
Speakers
Jamo 5.0 system $249 great little setup for apartment or small bedroom, much better then satelite systems.
Subwoofer
Acoustic Audio PSW-12 $148 or go here and bid $20 less, I am sure they would accept it.
Receiver
Sony STR-DH700 $219
all have free shipping and I only put you $16 over your budget... I hope that is cool, however you could go on ebay and haggle the sub.