I usally buy the Wally World Federal bulk 223. It's like $40 for 100 rounds, 40 cents a round.

For accurate rounds, I reload. Reloading the 223, or any rifle round, is kind of a PIA. I am finding the case length seem to make a big difference on accuracy. That means one has to trim each case. Also, most reused 223 brass has to have the primer pocket reamed a bit due to the factory pocket crimp. If/when you do start reloading it, do yourself a favor and add a Lee universal decappong die. They use a collet to hold the decapping rod, so rather than breaking counless decapping pins due to the crimps, you can just reset the pin (although I have still managed to break one of the lee pins).

A note to every body, sometimes cheap brass can be found at you local recycle center. There are companies out there that are contracted to clean out the military and police ranges and take the brass to the recycle center and sell it to them. Last time I went, I think it was like .13 cents per pound. You have to seperate it, inspect it and clean it, but it does keep the cost down.