Silver Bear 62gr, $0.28/round (low)
SS109/M855 5.56 Lake City, $0.80/round (high)
From gun-deals.com - User-Submitted Gun & Ammunition Deals
I know Silver Bear is not a direct comparison to SS109 LC, but that gives you the spread on ammo other than from CTD. I'm a big fan of LC ammo, but no way would I spend even 80 cents a round for milsurp. Selling on Gunbroker, you may get the near $1/round CTD wants.