from a test edmunds did in a flex fuel chevy tahoe. and it doesn't take into account the extra cost from the subsidies given to grow the corn for "cheaper" fuel.
E85 vs. Gasoline Comparison Test
Gas Result:From San Diego to Las Vegas and back, we used 36.5 gallons of regular gasoline and achieved an average fuel economy of 18.3 mpg.
Gas Cost: We spent $124.66 for gasoline for the trip. The average pump price was $3.42 per gallon.
E85 Result: From San Diego to Las Vegas and back we used 50 gallons of E85 and achieved an average fuel economy of 13.5 mpg.
E85 Cost: We spent
$154.29 on E85 for the trip. The average pump price was $3.09 per gallon
Gas/E85 difference: The fuel economy of our Tahoe on E85, under these conditions, was
26.5 percent worse than it was when running on gas.