I've burned over 300 gallons of E85 in the Sentra. and I do experience a small drop in mileage but it's usually 3MPG on my typical 30 MPG. so actually it saves me the smallest amount of money vs regular. where I REALLY see a difference is my engine knocks on less then 91 octane (like a V-spec sentras) and has a sensitive knock sensor.

If I "dose" 9 gallons of E10 87 octane with 3 gallons of E85 I get a 91.5 octane mix of E29 and it returns me close to 30mpg which saves me $33 cents a gallon over running Straight E10 93 octane. but on the highway I just fill up with Straight E85 since it's running closed loop the whole time and keeps the AFR's in check.

so if you monitor the AFR ratios you can actually save money, since you can lean up since most stock cars run rich.