For under $200 a sub your best options are Dayton Reference or Alpine Type-S. Both are designed for SQ, have good displacement capabilities, and work with moderate power and small-ish enclosures. Also you may want to consider a single 15 instead of dual 12's...usually a 15 will dig deeper. Someone was selling a couple SoundSplinter RL-P 15's on here not long ago...based off the legendary TC9 platform it will easliy out perform any combo of 12's mentioned in this thread.
My advice, grab a single 15, throw 800-100rms at it. Forget Skar and Kicker...Skar is garbage and unfortunately Kicker's quality has gone down hill over the last couple decades. Look to brands like Alpine, Sundown, JL, anything TC Sounds built, Image dynamics, Dayton Reference/Ultimax. Honestly the best value in subs right now would be Alpine Type-S...underhung motor/coil design, 15mm excursion, relatively shallow mounting depth, inexpensive, Alpine quality...and available in a 15.
Buy one of these:
http://www.caraudio.com/forums/subwoofer-classifieds/636401-fs-soundsplinter-15s.html