I think I saw some at the feed store for 35 cents each once. However... I mainly sell to friends/acquaintances so I'm not a real business. If you are, you will have to go with fresh cartons each time in most places.
Sad but true, it will be about 40c each if you don't buy them in the pallet load. But what will most of us do with 10k cartons? My customers recycle cartons.