Given the cost of reloading 12 or 20 ga. oneounce above has the right answer.
Just buy a flat of Remington Gun club, shoot em up and reload them up to 6-8 times per hull.
Like it sez on the shampoo bottle. Lather, Rinse, Repeat.
Probably about the same cost as buying empty hulls, as long as you take advantage of sale prices to buy the flat in the first place.
Formerly the best deal was the Sport packs at Wal-Mart. Those seem to have disappeared. The Remington Sport pack boxes of 100 were a great deal, and as long as you bought Remington you got the good Gun Club hulls.