what kind of car do you have?
500 will not get you great sound either and all the places are overpriced as fuck, but if you have to, try Best Buy.
Audiobahn subs and amps have never done me wrong

Kenwood makes some incredible highs

Do you have a stock head unit? If you do, dump that as well.
For 6x9's, I'd recommend Sony Xplod's. But stay far far far away from the Xplod amps and subs.
For your "roundy speakers" I'd say go with Kenwood, and you can't go wrong with Kenwood 6x9's either
Also, if you've got a day some weekend to spare, I'd recommend installing it yourself. It's not that hard and will save you a significant amount of cash