You can go cheaper on the CPU, RAM, and motherboard. Graphics cards will function on PCIe x1 slots just fine (as long as you're not gaming), you really only need one CPU core, and 4 GB of RAM would be plenty.
This is the board I use:
http://www.newegg.com/Product/Product.aspx?Item=N82E16813128566I've got six graphics cards running on it, all on PCIe x1 to x16 risers, powered by two 950 watt power supplies.
Cheap FM2 dual-core processor and 4 GB of RAM, Ubuntu 12.04 installed on a flash drive.
So, you could knock maybe $200 off your build there...