17.1 gallon tank
2 gallons E85 @ $1.73/ gallon
11 gallons 87 octane @ $1.83/ gallon
I'm assuming the last tank was 87 octane, I don't know because I didn't ask the guy I bought the car from.
% ethanol: 17%
Compared to buying mid grade at $2.07/ gallon, I saved $3.38 cents on the fillup, a 12% savings
Of course, it's not a pure savings because I'll lose a mpg or two on the tank. Ethanol doesn't contain as much energy as gasoline.