Cost of factory ammo: Assuming comparable quality loads is tossup. I haven't seen Hornady .308 AMAX any less expensive than Grendel AMAX. High quality .308 for hunting runs about the same as factory Grendel loadings for hunting.
You seek escape from pain. We seek the achievement of happiness. You exist for the sake of avoiding punishment. We exist for the sake of earning rewards. Threats will not make us function; fear is not our incentive. It is not death that we wish to avoid, but life that we wish to live. - John Galt