When my "Ammo Purchasing Club" buys, we pool together several thousand dollars which gives us some negotiating power. We have found our best deals with a particular seller that makes the gun show circuit in our area every couple of months. We usually fill the back of a pick up truck with the amount of ammo we purchase.
After running the numbers, we feel that at the current price of ammo, we will be much better off reloading. Back in the days when a case of .45 ACP was $180, it really wasn't cost effective to reload, in our opinion. Now with ammo more than twice that price and higher, we had to reconsider our options given the amount of ammo we shoot.