E85 quires MORE fuel to burn, which also means increasing the size of your fuel injectors and pump.
With the increased volume you'll consume, the cost of upgrading the fuel system - you won't actually save money from making the switch unless you're running a very extreme performance set up.
Short version: Don't do it if you think it's going to save you money. It will end up costing you more.
1998 Roush: M112'd Aluminum block 4.6L 2V 6 speed track car
1999 SVT: Mostly stockish
1970 Mach 1: Resto-modded monster
2000 Roush #5004 - World's FIRST M112'd V6 Mustang. Sold, but not forgotten.