Here are a couple links for you to read Nyksta
http://www.accuracy-tech.com/6-5-cre...08-winchester/
https://forum.snipershide.com/forum/...or-for-hunting
They kind of blow both your theory on ammo cost and barrel length out of the range.
I'll help you out here because it seems to be going past you without sinking in. What my point is, is that smaller calibers like the 6.5 and 7mm are getting the job done more efficiently than the 30cal's. It's not magic bullets in longer barrels, its science and technology.