Walmart .45 ACP is/was cheaper than anywhere else, if there is any on the shelf that is. This is before shipping and handling from an online distributor too. I was seeing $16-17 per 50 rds at AIM and Walmart sells it for 14.97 per 50 rds Blazer Brass. I think Walmart WWB .45 is also competitively priced too. Walmart handgun ammo is basically wholesale prices, you can only get it cheaper by reloading. Their rifle ammo prices don't seem as good though.
Also, for a while I was stuck buying .45 at Walmart because I had everything I needed to reload except primers. Walmart saved the day in that case too because I was able to trade a couple of boxes of Blazer 9mm for some large pistol primers. Now I won't really need to go to Walmart for ammunition unless I run out of reloading components before the craze dies down.
Other than that, Fed bulk pack .22 from Walmart is as cheap as you can get and still burn powder.