Dell PowerEdge R710 2x Xeon E5620 2.4GHz - $399
I have 10 of these servers available, all of them have 3.5" bays. They are all tested and in excellent working and cosmetic condition with barely any signs of use.
The price is for the base unit with the CPU's and no RAM. To add on memory, it will be $7/4GB stick or $15/8GB stick. I also have HDD's, price is dependant on size, send me a PM for details.