I have a Yamaha 10" sub, it's alright; I'm not sad that I bought it, but it is going to be upgraded. it can't handle the size of my room, and it can't touch 20Hz.
As far as BIC subwoofers, the nonprofessional reviews I have read have been positive.
At this price range I don't think that there will be to much that will get you too close to 20Hz, and anything that will get to 20Hz will be not be small.
As far as recommendations, Matt34 listed a bunch of good ones, but I'd like to add; Dayton's sub-100 (part no. 300-633) and sub-120 (part no. 300-635), also from Parts Express. They are cheeper then the Titanic kit Matt referred to.
The outlaw Audio
LFM-2, and
Aperion Audio Intimus S8, may be things to give a look too.