Considering your budget, I'll second Komskies suggestion.
Price match tigerdirect.ca's
$329.97 at any Memory Express location (looks like only the NE has any in stock at the moment), save $100 and pay no shipping. That's a pretty good deal for a capable 5.1 package system.
In addition to that, remember to
never overpay on cables and wires. monoprice.com is just one option here. (I've also heard that Superstore carries some decent, cheap electronics accessories)
EDIT: A little late to the game am I. :/