If you have a cheap jigsaw to cut the hole for the driver and plate amp.....
I offer you 2 options (different prices - same SQ - just different LF extension and SPL) that can't be beat by any retail option.
OPTION 1
Parts Express cabinet, 1 cubic foot, pre-finished, $125:
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=302-800
CSS TRIO 8" driver with XBL motor and 13mm linear one way excrusion(the best 8" sub around until you go to TC or JL W7 units), $85:
http://www.creativesound.ca/products.php?make=CSS
300 Watt O Audio plate amp, $160:
http://www.oaudio.com/300W_SUBAMP.html
Use some 3" tubing to make a 18"-20" long port with a single 90 degree band to fit in the cabinet.
Response down to about 30Hz, practically speaking.
About $400 total estimated price with parts/accessories/shipping.
Where else can you get a 14" cubed small sub with this performance for $400? I have no clue....
OPTION 2 (Super-Econo)
BTW, you can also pull this off for about $200 if you don't need so much SPL and can make do with a little less extension. You can buy the Dayton 8" powered sub.
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-631
It has a good cabinet and amp. Discard the driver. Install the TRIO 8 driver and install the appropriate port tube(3" diameter x 17" L). You will still get in room output, very clean/hi fi, in the 105dB range(with corner placement) from about 40Hz on up. Use extra thick acoustic stuffing to have smooth response with no peaks in this small cabinet. Cabinet 11" x 14" x 15".
-Chris