Want my advise, do not waste your money with lower brands. Because that's all you'll be doing, wasting your money.
Now, in my large amount of testing and trying out different stereo equipment, this is what I've come up with so far:
My favorite decks are Alpine & Pioneer because they give you plenty of control in an easy to control fashion.
For amps, you get what you pay for...I've tested out Pioneers, Kenwoods, Jensens, Rockford, Kicker, MTX, etc. I have to respect Rockford, but MTX and Kicker have worked better for me.
Subs...what can I say....I'm a huge Kicker fan. They've always worked phenomenal for me. Runner up has to be MTX.
To sum it up, $500-600 won't get you much anything that satisfy your ears. I recommend saving up some more, say $1000-2000 and maybe try something like I did. You can check out my page on cardomain, which you can access through my profile, for details.