Why not buy a board based on the Atom Denverton, like Supermicro's A2SDi-8C+-HLN4F and a separate 10G NIC?
That would at least be cheaper that $1200, and will have support for 12x SATA disks (so if you do not need a SAS controller...).
I'd say 150-200$ would be fair for this. If it was a supermicro board perhaps slightly higher.
This seems low, sure there are examples of very cheap Xeon D systems, like the HPE EC200's and the Quanta servers, but to me around $500-600 seems more reasonable at the moment. This is assuming it is used hardware, and because the board has both 10G sfp+ and a SAS3 controller.
Given buying from new, 1k is not far out, but I would absolutely consider getting something else (or buying used if possible).
I doubt a separate sas controller card will require much more power than one built-in on the motherboard, so OP could probably just do that.
EDIT: another option could be this:
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12x SATA3 and newer Xeon D (with only 4 cores, but better performance per core) and in general lots of network interfaces.