What are you going to use the rifle for? Plinking, go for the 223. Hunting, go for the 30-06. That is using the 2 rounds you listed. There are many more rounds out there to choose from. Cheapest rounds will be the 223/5.56x45, 7.62x39 Russian and 5.45x39 Russian. 308 Winchester/7.62x51 NATO is a very popular hunting and target round and probably a little cheaper to shoot than the 30-06.
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