I agree with jonnythan,
Fry's (outpost.com) has a sale on the polks all the time. Some weeks it's the r30 towers ($90 pair), the next week will be the r15 bookshelves ($40 pair), and occasionally the csi25 center ($69). That combo with the dayton would be very hard to beat for the money. I've heard the r30's and the r15's, and they sound good. At these prices, they are a steal.
The BIC's that Buckeyefan suggested is also a great value, but puts you out of your budget. Stretch your budget a little more , and this would be a great way to go.