I'd look at Hsu... Dual Drive VTF-2s:
The VTF-2 MK5 subwoofer is Dr. HSU's best value subwoofer. Deep bass that doesn't compromise, making it the best affordable home theater subwoofer on the market.
www.hsuresearch.com
Its a little over your budget when you add shipping, but the ultimate payoff is going to be the better option. Hsu Subs are by far the best bang for the buck. These will seriously outperform the PB1000s as a pair and come in affordably below the cost of 2 PB or PC 2000 Pros.
In short, these are Subs you can live with for the next 10 years and not be wanting for more!