In the price range you are looking at you owe it to yourself to check out the Rythmik LV12R
You can find a lot of information about this sub (as well as other Rythmik subs) at the "Official Rythmik Audio Subwoofer thread" here on AVS.
I had never heard of Rtyhmik until a year ago while shopping for a new sub. I had been looking at the Def Tech ProSub 800 & 1,000, Klipsch (SW110, 112 & 115) and a Martin Logan Grotto i ($1,800). ...