I have no idea. best i can tell you is e85 has to be around 27 cents cheaper for me to break even. 87 right now is $2.39 E85 is $2.19. It went up from yesterday. I get on average 14.5 mpg on 87.
You gave me the ingredients to find your answer. If you average 14.5 mpg on 87 and it costs $2.39 right now, divide the cost into the range and we get $.1648 cents per mile.
If your engine's performance is like mine, I reckon you'll average 10.9 mpg on E85 and at that price it would cost you $.20 cents a mile to run. Obviously not as cost efficient.
Put another way, if you were to drive 300 miles on 87 octane at that price, it would cost you about $49.50 versus $60 for the same distance on E85.
Your break even point with E85 compared with 87 @ $2.39 is $1.78, a $.61 cent difference, assuming your engine will average 25% less mpg.
Run two or three tanks and see how she likes it. One will not tell you much at all.