The biostar racing might be a great lower cost board. It will be around $250 according to this video - pricing is discussed at 1:33:
https://youtu.be/gETHFMf1fcU
Nice feature set:
http://wccftech.com/intel-x299-motherboards-pictured-asus-asrock-gigabyte-biostar-evga-msi/
Biostar X299 Racing GT9 Motherboard
Biostar is also preparing a very strong X299 offering in the form of the X299 Racing GT9. This is the flagship X299 motherboard from Biostar and features a full Extended ATX form factor with a yellow and black color scheme.
The motherboard features the LGA 2066 socket that supports Intel’s Core X processors and is powered by a single 8 pin connector. The motherboard itself is supplied power through the 24-pin ATX connector. The board has a 14 phase power phases that would allow higher stability and a lot of overclocking potential to enthusiasts.
This monstrosity also packs 7 PCIe 3.0 x16 ports (x16, x16, x8, x4, x4, x4, x4), a single M.2 port and also two U.2 ports. For storage we are looking at four SATA III ports which should be enough for storage enthusiasts as there’s also M.2 and U.2 support on board the product. On the board, we can see eight DDR4 DIMM slots that can support 128 GB capacities at speeds of 4000 MHz (OC+). I/O on the backpanel includes 2 USB 3.1, 1 USB 3.0, 4 USB 2.0 and Intel Gigabit LAN port.