It really depends on your budget. If you're not willing to go the distance and do it right the first time, then just go for ur basic sub and amp. K7's are pretty nice but expensive. JL's will give u the most and more for wut u pay. Amp's are more or less the same. I prefer rockford fosgates over most amps cuz i think the quality is much better. If you want to go all out and change the entire system, except for the HU of course, you're looking at $700 - $1500. 4 channel amps aren't cheap. If you want, go get urself a 5 channel amp so u'd power ur spkrs and a sub.