Define building one? Such as a AR platform or a bolt action? There are a few Howa Mini actions still floating around in 6.5Gren but if i was going with a typical SA i wouldnt be looking at the Grendel. You would be better off with a 260Rem or 6.5 Creed if you want to use readily available short actions.
Something like this would get you started in a mini action without breaking the bank.
https://www.brownells.com/rifle-part...rod113624.aspx