Sub for basement system

As a diehard Chicago Bears fan living in New Hampshire, I am working on setting up a TV room in my basement. The room is 22X13 and the ceiling is about 7 ft. I currently have a Parasound HCA 800 amp running through a NAD 7100 receiver. My speakers are a pair of Totem mites. I am interested in adding a sub to get more lower end. My budget is about 650 dollars, and I would like to purchase a used sub. Any thoughts?.
I have M & K V-125 12" Powered Sub. Retailed over $800.00. I will sell for $490.00 shipped to your door. One year old. Go to the M&K website and read where this sub in Sound and Image Magazine face-off RANKED it # 1 against 17 other subs in its class. E-mail me and I'll send you the pages. Let me know?!
Go to your local circuit city and pick up a Velodyne ct-120 or the ct-150 you will be truley amazed. Look up the spec's. at, good luck.