Some quick searching yielded a little over 50 cents a round for 308 Santa Barbara surplus. Wideners and others have 150g Korean surplus 30-06 for a little less than that.
Hunting ammo price difference doesn't seem like that much, so I wouldn't let the price of plinking ammo keep me away from a caliber, and the '06 might even be a little cheaper if you stock up. Reloading components aren't that different afaik.
300 win mag, other magnums, yeah the price of ammo goes way up.