For .223, I pay around $.30 a round, and that’s on stripper clips. I also buy 900-1,000 rounds at a time.
For GOOD .308, expect around $1.50-1.75 a round. In one of my recent mags, they were shooting a short barreled .308 bolt action with the Hornady TAP in 155gr, and were doing 1/2 MOA 5-shot groups. The 168gr was hitting 3/4 MOA in 5-shot groups. You can usually find that ammo for $27-30 for a box of 20.