You could run a number of home-built subs off those amps.
That would give you considerably more boom for your buck than storebought. Have a look at the diy forum at avsforums, kits and plans offered by Madisound, Parts Express, Zalytron, and Creative Sound Solutions. If you don't mind a sub that you'll never want to move, see the TC12(?) horn plans at Creative Sound Solutions. There is probably no more bass for the buck than that. And if circumstances change, you could always put the woofer into a more civilized box and still enjoy decent bass.