At the local wally world .223 is almost always available. $5ish/20 for tula $10ish/20 for eagle or some such and $69ish/50 M885.
.243 is a lot harder to find, there might be s box or two once in a while. IIRC it was $15ish/20 for some redbox stuff with an eagle on it (can't remember exactly and I think $17-23ish/20 for some rem.
Might want to browse the stores near you ammo shelves for a couple weeks and just see whats available. Early mornings are usually good for the best pickings if you have the time. The next closest wally world is near a much larger city and their ammo shelves are almost always bare, so YMMV.