If you want something pre-made Q-logic makes a great sealed box that they sell at places like best buy for less than a $100. It something to think about if you don't want to build your own. Once you find a sub that you want you just need to look at the volume specs for the sub. I would think that most 12" subs in a sealed box (not a high excursion sub) would want a box of about 1 cubic foot give or take .25 cubic feet.
I've heard really good things about the Alpine Type-R subs. A 12" shouldn't run you too much more than the one you mentioned.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewI...5711536427&rd=1
Thats' a dual 4ohm voice coil model.
I've got s 12" Pioneer IMPP dual voice coil sub in a Q-logic 1.25 cubic foot sealed box in my trunk. I put the back of the box up against left rear seat with the sub facing into the trunk (towards the rear of the car) For maximum bass just fold down the left rear seat-back.