You thought about 6.8 spc or 6.5 Grendel in AR15?
If not dead set on AR 10 platform, it may be help you shave quite a bit of weight and cost.
You could build a 6.8 rifle for less than $600, and add a custom trigger for another $200, and still have less in it than an entry AR10 with milspec trigger and furniture.
I built a 6.8 to hunt with this year. It's chronicled in a thread in the readloadinng/firearm section.
Dropped a 200# 8pt in his tracks with a 110 grain Nosler Accubond shooting under 1 moa in my rifle.