Q6600 is only $300 at Fry's right now. Lowest I've seen lately has been about $475 at Newegg. If you live near one, you can get a motherboard included.
http://shop1.outpost.com/product/5101696
Quad Core CPU
Now it's $273 + shipping.
Rumor has it, there's another price drop happening next week.
Rumor has it, there's another price drop happening next week.