BTW, 6 Polk R15s + the Dayton Sub-12 would be just above $300.
The R15s are on sale for $50/pair from Frys.com
The matching center, the CSi25, is currently $70, so 4 R15s + 1 CSi25 + 1 Dayton Sub-12 would come in under $350, but Frys is currently out of stock on the CSi25. They do let you preorder though.