This is going to be "build your own" btw but anybody who's used a philips screwdriver can do this. Here in UK I have the total mentioned above at just over 2200 GBP including PSU and a cute Corsair case (http://is.gd/0pfKhg) so we're talking 3300ish dollars leaving 200 left for a pro mech KB and mouse. For the ram I had Crucial supply me for 780 british pounds (1200 USD ish) for 128 GB of 2400Mhz DDR4 ECC DIMMs (4 x 32 - there are only 4 slots so don't do 8 x 16), which works with these boards. As I said total including RAM about 2200 pounds so 3300 dollars. Or if you don't need 128GB start off with 64, say, but stick with the 32GB DIMMs so you can upgrade later.
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&DE...
Asrock Rack made some nice boards with onboard IPMI, dual Intel gigabit NICs, and 8x SATA. Kind of pricey but still under $500 for the board back in 2013. Been a great board: http://www.asrockrack.com/general/productdetail.asp?Model=C2...
Here's their Xeon D stuff: http://www.asrockrack.com/general/products.asp#Server
Denverton is the successor to Avoton; 16 cores, 16 lanes of PCI-E v3, 10GbE, DDR4: http://www.fudzilla.com/news/processors/39156-intel-s-denver...
Haven't heard anything about it for months, though.
I will have to consider this. I run a Mini-ITX board in a Micro-ATX case anyway. Perfect form factor.