This website shows the average percent spread in prices between e10 and e85 per state. The average price spread across the country is 17 percent. Compare that with the expected lower economy of 15 to 27 percent, and the majority of cars will cost more operating on E85.

Popular mechanics reports it only being worth using in topping off a rental car. The calories per gallon are 30,500 for e10, and 22,900 for e85. It's kinda' hard to argue with solid data.