The also have an 1800w dual 10" driver sub for $500. I haven't got a clue if it's any good but it's interesting.
Link
Power rating: 1800W
Impedance: 22k
Woofer: 2 x 10" aluminum cone woofers
Frequency range: 20Hz - 200Hz
Cabinet: closed
Boundary Gain Compensation filter
Continuously variable level, phase, and cut-off frequency controls
Motional Feedback (MFB)
Front- and rear-firing subwoofer
Dimensions: 15.4" W x 17.6" H x 17.0" D
Weight: 55.1 lbs