Tank #1

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%

Octane: 88.5

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.