Five shots from that brass is definitely the maximum for cost planning purposes.
The rule of thumb for semi auto rifles is "four reloads then chuck it" for brass. This came out when Garands were firing 30-06, but remains quite valid now that AR's are shooting a bunch of stuff.
Having been on the range when a reload ripped in half leaving the forward shoulder in the chamber, I agree with the conventional wisdom when it comes to feeding my ARs with reloads.
Machine guns are awesome until you have to carry one.