bigbangtheory 5,000+ posts
CarAudio.com Veteran
With a small budget like that, I would suggest buying used around here. You'll be able to buy much nicer equipment with limited funds. Here's how I wold break it down.
HU: Pioneer P660 $100
Amp: Elemental Designs Nine.5 $350
Components: Pioneer TS-C720PRS $250
Rear Fill : Pioneer REVs $75
Sub: Phoenix Gold RSd12D $110
*That leaves you with $115 for wiring and building materials. Build your own ported box for the sub, to get more output for the money. Plus, you won't have to pay some shop an outrageous amount of cash to do something you can do on your own.
Have fun.
Basically what I mentioned without going to the classifieds, because I am too lazy to look stuff up, lol!