I'm looking for a good Bang for the Buck Sub

I'm about to move into an appartment and I'll need a little more low end than I have in my room I think. I already have a pair of older towers (not sure what brand) with a 12" woofer and 10" PR in each one. These are good for movies and the like, but for party music they're a bit lacking. I'm looking at grabbing a single 12 or 15 that I can amp off one of Parts Express's plate amps and stick in a non-intrusive box. The average home subwoofer enclosure would be fine, maybe a little bigger. I dont' want to do any complex designs. I may port it, but I'll probably run with a sealed enclosure. I'm also thinking on a college budget here. Try to keep it cheap, but not poor quality. What do you suggest?

thanks!
 
I have an old skill saw in the garage and I use my Dremel Advantage as a router all the time. I have the attachment for it and all. I'm really not the best with wood, so I don't want to have to build something too complicated. I've always felt more comfortable working with fiberglass (which I still may do for this little project)

I completly forgot about the tempest. It's said to be one hell of a sub,but I haven't heard it. Are there any cheaper subs that will compare?