TLSGuy linked SB1000Pro, at $599, double of OP's budget.
Here's a much better option for much less money and MORE sub:
SBS PB-1000 (non-Pro) at $399 with free shipping it's practically a steal.
Ported box home theater subwoofer with 10-inch high output driver and 300 watts RMS, 700+ watts peak power amplifier, the PB-1000 delivers ground-shaking SPL output and subterranean low frequency extension without sacrificing detail and accuracy.
www.svsound.com