speakers come in pairs, so you will only need one pair.

so figuring you would then have 200 (ish), you can certainly find a nice 4 channel amp and run the fronts for the time (channels 1/2), and come in with a subwoofer (bridged to channels 3/4) when you can afford one.

edit: btw, i love those Polk 6.5's. got a pair a while back and they rock