I'll bite since I actually own rifles in both these cartridges. Match ammo is absolutely cheaper in .308 than 6.5 Creedmoor. With 6.5 Creedmoor you're looking at $23+ for a box of 20 rounds. It's not too hard to pick up 3.08/7.62 FGMM for $1/rd. If you're okay shooting Prvi you're looking at 70-75 CPR depending on the amount you buy.
.308 bullets are also more reasonably priced. Hornady got rid of their 6.5 140 AMAX projectiles and now their ELD-M/ELD-X bullets are priced a couple cents higher, 33+ cents per bullet. You can get Hornady 178 BTHPs (only slightly lower BC than the ELD-Ms) or Nosler 175 RDFs for 29 cents per bullet. Obviously if you're shooting Juggernauts or something the price will be higher, but it's not like 140 Hybrids are cheap either.
Let's be real and say that mostly everyone who shoots an intermediate 6 or 6.5 uses H4350. For .308 the range of powders people realistically use is much greater and so you have a better chance to pick up some powder at a discount. For a long time Long Range Match surplus powder was available and you could get a great deal on 8# kegs.
We'll avoid the price of brass since you mentioned using .308 brass and of course primers are the same.
The big thing really is barrel life though. We can be generous and say a 6.5 Creedmoor gets 3,000 rounds of barrel life. Without threading the muzzle, a nice barrel and chamber/install might be $600. That's about 20 cents per round of barrel life. We can be conservative and say a .308 gets 5,000 rounds of barrel life. For the same price of a barrel and install, that's about 12 cents per round of barrel life.
6.5 is obviously ballistically superior to .308, although the difference isn't as drastic as people make it seem. It obviously also recoils less than .308, although I don't think the difference there is as drastic as people make it seem either. I've shot our 6 Creedmoor, 6.5 Creedmoor, and .308 rifles, all similarly configured, similar in terms of weight, braked, shooting similarly stout loads back to back to back on numerous occasions and 6.5 IMO recoils only a little less than .308. It's 6 Creedmoor that really offers a sizable reduction in recoil. Those are the two main areas IMO where 6.5 Creedmoor is better than .308, but I don't think it's better than .308 at everything. I think .308 is better in terms of ammo options (FMJ, specialty ammo, defensive ammo, etc), factory rifle options, barrel life, and yes, price.