that sucks, but isn't going to stop you.
the css trio12 looks pretty good.http://www.creativesound.ca/details.php?model=TRIO12
it appears to actually be a better driver than the other one (xbl and shorting rings, should be very clean) but you will need TWO drivers @ $159 each.
with the two twelve's you can make the cab slender and taller and/or you can go with a cube and mount one driver on the front/back and one pr on the left/right side, whatever works out to six cubic feet net. this will cancel out all vibrations. you could even put the pr's on the front/back and the 12's on the sides if you like the look of the big pr's staring at you.
you will probably lose a couple of db at 20 with the dual 12" option because of how you will wire the amp, but pick them back up up high because their sensitivity is higher.
edit: the 21" FTW (specs seem to have changed again), but it still looks like it wants a really large ported cab, 14 cubic feet or so. not the best choice for 6 cubic feet. it will actually produce less bass at 20hz then the other options.