Yea i second that. If you're looking into an amp to power ur speakers x 4, $100 isn't going to do the trick. A decent 4 channel amp, you should expect to pay around $300. Something better, expect it to be around $500. But with the speakers you're running, i'd go for maybe an mtx, fosgate or even kenwood. Those aren't that bad.

In terms for subs and amp, u really gotta look into that. Gots to see what you like. An amp compliments the sub and vice versa. Good luck man!