A gallon of E85 has about 72% of the energy of a gallon of straight gasoline. So from a cost perspective, E85 needs to be 28% cheaper per gallon to be worth it. So at today's average of $3.85 per gallon for regular unleaded, E85 would need to be at $2.77 per gallon. But its average is around $3.52.
If you figure prices based on the energy you are buying, you would have to buy $4.50 worth of E85 to get the same energy in $3.85 worth of regular unleaded.The Daily Fuel Gauge Report from AAA
has some of this converted price data as well (using different/better figures than my theoreticals above).
BTW, if we only consider cost, Diesel beat regular unleaded in terms of dollars per unit of energy even with the higher cost per gallon.
Edit to reply to latest post -- Ethanol _CAN_ be bad for engines in that it attracts water. And water in an engine is a bad thing indeed.
And for net environmental impact, numbers I have seen say it takes 1 unit of fossil fuel to create 1.3 units of Ethanol fuel. So we are right at or even just below the break even point of energy per gallon.
We insert the plants we turn into Ethanol into the carbon cycle to remove some of the greenhouse gases we burn, yes, BUT burning Ethanol produced Ozone that we don't get when we burn gas.
To me it just seems like a lot of effort for a little gain. Especially since we are diverting corn which could be used for food into our gas tanks and then people complain about the cost of food.
If we used sugarcane like Brazil does, then it is a different story since they get back like 8 times as much energy instead of 1.3 times.