an xxv olm 1612 will cremate a treo all day but they want 1600 to 2000 rms and are amazing sql subs especially in your box specs. they are about 225 new with warranty shipped (if you buy from me) or about 300+ at ocs
OLM are not SQ by any means...if you buy used you can afford alot more...no sense in buying brand new when you can get them reconed for cheaper than buying a new sub...
If you can make a new box why not go with the Mag?? Make yourself a nice sealed enclosure or buy one from walmart for $30.00, like I said before they only need 1 cubic foot sealed per sub plus they have a really shallow mounting depth at 4.75". You can save yourself the guess work and save some some room in your trunk. Makes sense to me especially since its in your budget. Check the specs out for yourself here. http://stereointegrity.com/mag.php