Cheap sealed subwoofer

infinity reference 1262w, about $60 low cost.

alpine swr-12d2, about $120, but has about 50% more excursion and is a better driver.

a single 12" sealed isn't going to be too spectacular for home theater.

Dayton DVC on sale for $99 would be really hard to beat if you're not limited to 12's.

Go for the Dayton. The others will not be as satisfactory with movies.

I'd go with an 18" cube if you want something small or bump it up to a 20" cube if you can fit that.

Go ported if only using a single 12".
How about one of these http://www.parts-express.com/pe/showdetl.cfm?partnumber=295-464
One of these http://www.parts-express.com/pe/showdetl.cfm?partnumber=268-352
One of these http://www.parts-express.com/pe/showdetl.cfm?partnumber=300-750 or this http://www.oaudio.com/300W_SUBAMP.html
in a 3.5-3.7 cu/ft box
If you want sealed go multiples of 2-4 subs or as said above a 15"or 18".

While I can't comment on the price, I wouldn't buy it for the box. The driver may be easy to repair (get it air tight... I'd try craft glue with tape to clamp), but it's a ported box, so you'd either need a matching driver, or a plug in the port (make it sealed).

If you aren't aware, speaker acoustic characteristics are described by "Theil/Small" parameters. These parameters are all you need to predict a woofer's response in many applications, like ported boxes. That's what makes driver replacement problematic - matching T/S parameters. In sealed boxes, it's not a factor, thus the advice to plug the port.

As to the value, consider these flatpacks - a very good value for what you get!
http://www.diysoundgroup.com/flat-packs-1/subwoofer-flatpacks-2.html

Have fun,
Frank