O wow. My dragon is 12" and will only eat about 7-8 3/4" dubia per day (if I try to pester him with more, even at a later time, he'll just turn his head away and get mad at me). This sounded low to me, but the vet says he looks just fine.
I supplement with butterworms and waxworms and crickets. Bulk crickets are definitely the cheapest feeder I've seen - though they're a bit harder to keep than dubia. However, since crickets are not as much meat, I wonder if the cost would even out or exceed.
O !!!
Turkish roaches ! They're a little harder to keep than dubia - but they are much cheaper. My friend has gotten them from here :
http://www.gulfcoastcrickets.com/. They are faster than dubia and can climb better - however, my friend uses a ring of packing tape or two around the top of the tub and she has never had an escape.