Gallons of E85: 5.575
Cost/ gallon E85: $3.049
The rest of the tank was 93 octane Amoco Ultimate
Octane/ tank: 95.378
Ethanol/ tank: 30.396%
Because I just topped off the tank, I don't have a good feel for what I paid for the 93 octane gas. However, at the time I filled up with E85, premium gas was $3.54 a gallon.
The rough cost savings of just the E85 fuel was 50 cents a gallon times 5.575 gallons, which works out to be $2.79 a tank.
I will update this with the mileage/ tank at the time of the next fillup. Mileage so far is 22.6 mpg.