I agree with lsiberian, if you're willing to do some wood working (IE making a box... can't be too hard.................................. right?

) then you could buy a pair of these
woofers and power them with a pro amp. This sort of performance, professionally, would likely run you around $2000 internet direct, and around $5000 at a hi fi shop. You could probably do it for around $500 including MDF, an amplifier, 2x woofers. Throw in a bit more for some laminate, or maybe primer and paint

and a bit more than that if you're thinking pretty exotic veneers (I... don't recommend it though)
You'd be getting those drivers AT COST, so the performance is even better than DIY performance is supposed to be!