for about $250 for the sub and driver... THT is unbeatable... box size is about 18 cu ft though (Gross).. add in a $100 plate amp and you're good to go.
as LTD02 said, it's a trade off you can't have "cheap", "small" and "powerful" all in the same picture. choose 2 of the 3 and you get the picture. you can do
cheap and small, but powerful is def gone
small and powerful, but that really jacks the price up as you get a much more powerful amp and drivers that can take a beating in small enclosed boxes
cheap and powerful,,,,,, and of course size goes right out the window.