i found a boss, lanzar, volfenhag, and a legacy for that or cheaper on ebay. the boss looked like a good one but its probably the best u can get for that price. and i dont know much about volfehag.
I would look into something like a jbl bp600.1. You can find them on ebay for about $150 and get a true 600+watts rms, instead of purchasing some bottom brand thats claiming 800 watts.
Ok people, Danny, Volfenhag makes decent subs and speakers, however, I wouldn't trust their amps, as they don't even offer a mono amp. If you need 800W cheap, look into an Audiobahn A8000T, hurry though, since they are not making them anymore. They just stopped producing them about a month or so ago. REALLY good amp for the price, I have one with two Volfenhag subs.
Boss, Lanzar, and Legacy all tell lies about their output, and if you need cheaper than that A8000T, then I would pick the Volfenhag over the rest of those.