For .223 I usually get the cheapest steelcase I can find. For 9mm, 45ACP, .22LR and bird shot I try to find Federal value pack at Walmart. Of course I do pick up higher quality ammo from time to time but have good luck with the mentioned cheap stuff.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek