you can get 2 L7 12's for 400 total. some other subs you could look at are jl's, i don't care for them much, just a personal preference, but you could also look at id max, rockford hx2, treo's bottom line sub..i think it's the ts....i'd go with the ss though if i was on a limited budget. for amps you can look at mtx 81000d, jbl1200.1, kicker kx1200.1, cadence a7hc, phd2, concept d1200 or d2400. there's many others as well. email me if you want some other alternatives
2 L7 12s with a jbl bp1200.1 will put you right around the 750 mark(including shipping) and also gives you LOTS of boom.
go to ebay....EBAY IS THE KEY!!!!!!
rockfors power hx2s, audiobahn 1205x, jl audio 12w3, alpine type r, soundstream spl or exact, orion hcca (b stock), infinity perfect, cerwin vega-vega series...just some off the top of my head.
amp wise the hottest thing out right now is the jbl bp1200.1. its cheap (270 + shipping), gives you close to 1400 watts at 14.4 volts, gives off full power at both 1 and 2 ohms whichs means you have a TON of wiring flexibility and its reliable.