u can get orion xtr 1500 for $226 or so, they been killin it on dynos., maybe not as clean as they once were but strong.. u can get 2 amps like mine for $300 1 per sub 930 rms @ 2 ohms..
Or for 200 bucks...there's always this * NEW * CAB-1600.1 Amplifier - Car Audio Bargain 5 star rating, 118 reviews. Amp has already been proven itself over and over again. Best sub amp deal on the market right meow.