no one has mentioned it yet but, 2 treo SSI's would fit the bill, 750-1000w each and they get LOWWWWWW like deep in the 20's high teens low
its been mentioned but mach 5 IXL line, you can get 2 12's for less than 500, will take 2000w and they get low too, or run a single IXL 18, its actually a popular home theatre sub and will get deep into the teens
and the havoc, either 15 or 18, will take 1500w all day and they get low
i know im going to get bashed for this, but my hdc 12 us in 2 cubes at 38 hz and hits the lows with serious authority. i think strass his 147db @ 31hz with 2 15's in 8.5 cubes @ 38hz