Sometimes biofuelsdigest.com has some useful insight and data, but often it can be said in two sentences rather than the several pages they try to fill. So check out this page of a recent post and importantly the chart:
They use the prices reported from http://www.e85prices.com and a study that estimates the mileage reduction from ethanol vs gasoline to adjust the prices of various blends and see what the “best deal” is:
As you can see, some interesting results.. E20 (20% ethanol) is the cheapest.. but there is not a clear trend in either direction.. E40 is actually the worst deal, and E85 comes in 4th.
Also note that straight gasoline would seem like a better deal that the current blend of 10% ethanol, but we need an oxygenate to prevent smog and incomplete combustion etc.. and ethanol is way better than what we used before (lead and MTBE)!
If you are curious about whether those E85 prices are actually really cheaper that regular gasoline on a mileage basis, http://www.e85prices.com/ has a calculator, but it varies so much with different cars, that one must calculate the MPG for their car on both fuels and determine what their break-even point is.