The price difference really needs to be at least $0.50 cheaper for it to make sense. In Denver, E-85 is about the same price as regular gasoline. Maybe $0.10 cheaper. It's not worth it because your MPG goes down around 17-20% when you use E-85.
The REAL way to go is natural gas. There's an abundance of it, it's WAY less expensive and cleaner to not only manufacture, but burn. I'll try to watch this documentary this weekend. Looks interesting.