It has been quite a long time since I owned anything with a warranty!
That said, fuel systems have been ethanol resistant since 1989 so whatever I have from then to new enough to have a warranty, I wouldn't sweat any ethanol fills. The OEMs simply don't want to have their stealerships flooded with people crying about CELs, even though the CEL is simply saying "Oops, Mr. Computer has maxed out the fuel trim and Mr. O2 says it still isn't quite rich enough!"
But you've STILL ignored the aspect I was talking about. :/
Yes, that would be the cost per mile or cost per gallon or just plain cost.