I don't know if you are still interested, but I noticed a premade bamboo cabinet you can get for a 10 or 12 inch driver for a very reasonable price.
http://www.diysoundgroup.com/bamboo-sub-enclosure.html
It seems to be made specifically for Dayton drivers and such, but I wonder if you might be able to get a Rythmik 12 inch driver and amp to work with this? On the Rythmik website you can get the amps and drivers seperately, to go the DIY route:
http://www.rythmikaudio.com/products2.html
If they did go together without any problem, this would be a cheap way of getting what you might want, although you are limited to the 12" sealed design. Also you would need to finish the cabinet, which sounds like it is labor intensive. I would love to have a subwoofer in the cabinet to match my natural Sierra 2s, but I don't have the extra money to put into it. Since I have such a large room open to other areas of the house, I need to go with a larger ported sub, like the Rythmik FV15HP and I definietely don't have the extra money to get it finished in bamboo.