Subsonic ammo being fairly available for 308? Absolutely. I can think of 6-8 manufacturers off-hand.
Ammo, like the rifle you want to be built, is purpose driven. You'll either have to design it to achieve your intended purpose(s), or pay the inherent cost of something ready-made to do so.
I shoot nothing but premier match ammo in my guns, so for me, everything else is pretty much dirt cheap in relative terms.