IMO your budget isn't large enough for 2 12's.
I'd go back and re-read 2kChevy's advice, it was by far the best you have received in this thread.
If you go the route you outline above it will be a complete waste of your money.these subs: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=270151957917&ssPageName=STRK:MEWA:IT&ih=017
and this amp: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=250130800976&ssPageName=STRK:MEWA:IT&ih=015
And will this box do well? http://www.circuitcity.com/ssm/Bass-Slammer-Dual-Vented-Subwoofer-Enclosure-BS212V/sem/rpsm/oid/119725/rpem/ccd/productDetail.do#tabs
I'd go back and re-read 2kChevy's advice, it was by far the best you have received in this thread.