To make alcohol you need to heat the mash to the whopping temp of 173 degrees. All around America is industrial and power plants which generate heat at or greater than 173 that has to use cooling ponds or towers to lose their heat.
According to one study. An acre of U.S. corn yields about 7,110 pounds of corn for processing into 328 gallons of ethanol. Now that same study predicted that the farmer used 140 gallons per acre to harvest but that is bull. We used to grow corn and you would have to have an oil tanker to grow 30 acres at 140 gallons. Five to ten gallons at most per acre.
Besides most farmers use diesel instead of gasoline or ethanol for their tractors and the cost for growing and harvesting is going to happen if the stuff is grown for fuel or for feed. Most of the mash not used for fuel will be sold for animal feed.
It has some problems like transportation costs but it isn't unfeasible.
I averaged 6 gallons of fuel per acre for field trips last year on my corn acres.