$500 for a "surround sound" system is, IMO, not really worth it.
If you're frugal, you can find a good deal on some L/R speakers for maybe $100, a center channel for maybe $150, some surrounds for $80, and a sub for about $200.
That's piecing together a system from various and eBay, though. Anything you buy in a box for $500 is, IMO, not really worth the money you spent.
$1000, all at once, will get you a *****in audio system (5 speakers + sub) from SVS. Add $200 or so for a receiver, and for $1200 you have a great system.