ok and you said your lookin for 12s or a 12 so what about an alpine type r 12 2+2 dvc 2 ohm- around $120 with shipping from ikesound.com
some knuconceptz wiring
KnuKonceptz - view products for category AMP INSTALLATION KITS
pick one at least 4 gauge or lower.
along with this amp
Hifonics BXi 1210D Mono Subwoofer Amps Car Amplifiers Car Audio and Video - Sonic Electronix for around $250 with shipping.
250 amp
120 sub
30-60 wiring
so approximately $420 which should leave more than enough money for a box if your planning on making it your self.
The reason why I recommended that amp which I know is more than enough for that type r is because if you plan to upgrade later you could just swap subs instead of your whole system.
just be careful with the gains on that amp if you decide to go with something similar to this set up. also recommended the dual 2 ohm model of the type r to get that amp to 1 ohm to take full advantage of it.
Don't give me crap for recommending type r's. they can be very good budget subs which is what he is looking for.