Grendel ammo and AR uppers appear to be available at Centerfire - surely they are going to be found elsewhere too?
Centerfire Systems, Inc. - Search
Regular Price: $18.99
You Save: $9.00 (47%)
Part Number: AM65503GL
20rd box Wolf 6.5mm Grendel Soft Point Brass Case 123 grain Non-corrosive Boxer primed Must be 21 Years-Old to Purchase Proof of Age Required
Part Number: ARUP-65-20 A3
Complete upper including the bolt.
All standard AR parts and accessories can be used on this upper.
That ammo is right at .50 per round, which to me is acceptable for a target-grade rifle.