I was in Mike's yesterday, I'm thinking they had 223/5.56 for about $5.50 a box/20, maybe more/maybe less. Didn't look at the name brand, if it was steel or brass. I'm sure you can call and ask to see if they still have it. 850-478-1129
I picked up a box of the federal value pack the other day, Walmart usually has perfecta ammo for .3 cents a round but all wal marts seem to be out of it. I prefer to do business with local shops but most are 50 cent a round unless you buy in bulk which is a little to rich for my taste.
Thanks for advice about mikes, but they aren't gonna see a dime from me after a couple of experiences I've had there.