found another article that does a simple comparison between economy, premium, and super premium dog food.
"The Premium foods studied had an average of 22% crude protein and 10% crude fat. The Super-Premium dog foods examined had an average of 27% crude protein and 15% crude fat. The Economy brands averaged 20% crude protein and 8% crude fat.
The Super-Premium foods suggested feeding an average of 1-3/4 cups of food per day for our 40 lb dog. Premium brands recommended 3-1/4 cups, while the Econo brands instructed feeding 6 cups a day."
source:
http://www.gooddogmagazine.com/dogfoodcosts.htm