If your budget is limited, I would look into buying a used sub. Many can be bought for less than half of what you want. I know of a Velodyne servo 10 inch that is currently sitting at 222 dollars. It also sounds like you should stick with a sealed sub. because they tend to be tighter. Even though the Hsu is ported that is the best option if you want new.
Subwoofer blues
I need help with narrowing down my sub woofer choice. I have $600.00 to spend and am not sure to buy used or new? My system consists of b&K AVP 1000, Citation 5.1, b&w dm620's and a nakamichi mb-10 using a x-dac. I listen to music but watch a lot of movies as well. I have listened to b&W and a few others but the bass seamed sloppy. PLEASE HELP Best regards Jim