E85 is a fuel with 85% ethanol and 15% gasoline.
It got pretty high RON value (about 105 or something I think) but it contains less energy.
So a car running solely on E85 will use about 30% more juice. But in most places the E85 is cheaper, so it will cost about the same as running with gasoline. Maybe a bit cheaper.
We have numerous cars here in Sweden which has been converted to E85 from regular gasoline.
You could also need bigger injectors and a remap to cope with the extra fueling.
Make sure the fuel-hoses and fuel-pump will survive E85 usage.
Some types of rubber and fuel-pumps will wave the white flag with this stuff. Depends on what type of material the manufaturer use from the beginning.
I would suggest you talk to someone with more knowledge about this before attempting it though. But I know of several cars running with E85 here in Sweden with no issues. It's a little bit harder to start when it's really cold outside, but on the other hand, you could wind up the boost alot without knocking
I considered doing this conversion a while ago. But then didn't want to risk it. But we have 98 and 99 RON here readily available. So I really didn't feel the need to do it either.
But as I said before. I would recommend more research before attempting it.