I just found 1,000 rounds of Aguila brass 55gr .223 at AIM Surplus for $299 plus $24 shipping. Considering recent prices, this looked good to me.
http://www.aimsurplus.com/product.aspx?item=AG223FMJ55&name=Aguila+.223+55gr+FMJ+50rd+box&groupid=21
http://www.aimsurplus.com/product.aspx?item=AG223FMJ55&name=Aguila+.223+55gr+FMJ+50rd+box&groupid=21