.308 isn't expensive if you reload.
My load off 20rds consisted of:
old .308 brass: $0
125grx20 RemPSP .30: $2.00 (Midway,TNT,etc)
51grsx20 WC846:$ 1.58 (Wideners)
CCI primersx20: $.30 (gunshow)
Total cost of box of .308 varmint ammo: $3.88
Sure, I could do it cheaper in .223, but that explosion of fur or feathers wouldn't be so large!