I have 2 Diamond Audio 12" D4's for sale in the classifieds section. I'd say theyre in your price range and would definately do the job. 2 of them sealed is usually the way to go, i've used them in sealed AND ported enclosures.
Each sub takes 600 rms and 1200 max
I aslo have an amp that would work well with them but it would take a lot of work to get your car prepared to draw that kind of power. A newer hifnocs brutus amp would power them well for cheap.
heres a link to em
http://www.caraudio.com/forum/showthread.php?t=294090
