I don't know what kind of sound you're looking for, but the second loudest setup i've ever owned was a set of 15" american pro aluminum cone subs off of
ebay for $88 shipped for the pair.
They sounded like complete poop, but the only setup i've had that was louder was when i had 1800rms from a lanzar optidrive hooked up to 2 L5 12's for about 10 minutes before i blew both of em //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif So i don't know if that really counts.
It could have to do with things remembered seeming grander than they were, or the excitement of my 1st system, or the amount of cheap seedy weed i smoked in high school, but i remember them being even louder than my 15" L7.
Edit: To be fair, the american pro's didn't sound THAT bad, the transient response was excellent in the sealed box, they just didn't sound that musical. They stayed on beat, tho, and seemed to go along with the tunes, you just couldn't count on them for actual reference, or knowing what notes were actually being played.