What 5.56 brand did you buy? I bought some Hornady in .223 but that stuff is like a buck a round.
PVI 5.56; AIM has a great deal on LC XM193 and Centurion .223 (I just recieved my shipment of the Centurion).
Remington UMC and Federal ammunition are fairly cheap at Walmart. You should be able to get ammunition for about .40-.50 per round. Hornady ammunition is most likely match-grade, which you don’t need unless you’re hunting at 200 yards or more or shooting in competition.