I reload my own but Estates and Rio's are cheap shells. I prefer to buy Rem. Gun Clubs because I think the quality is better and the hulls are reloadable.
I buy Federal Top Gun. A good shell at about $55.00/Flat (10 Boxes of 25). Usually found on sale at the bigger sports shops.
Reloading is a great way to make em cheap though :-)
GO TO WALMART $4.77 A BOX. I CAN'T RELOAD THEM THAT CHEAP.
Not sure if this is an option, but many times, a group of us at my club will go in together and buy shells by the pallet. Many times, a distributor will give you a better price for huge volume. Sometimes, they'll even throw the pallet on the truck that delivers the clays to the club for no extra shipping charge. Other than catching sales at Dicks, Gander Mtn etc, good cheap ammo is hard to come by.