IANAF: (I am not a Farmer, but I do live in Iowa) - Uh, the kind of corn you buy "on the cob" and the type turned into ethanol are not the same. Ethanol is made from "field corn" aka Yellow Dent corn. It's not something you want to eat in its raw form, and it's harvested by combines. Corn on the cob is made from sweet corn, which is not used for making ethanol. Popcorn is yet a third kind of corn...
Now, the prices of various crops can affect the prices of others, but it's just because farmers may decide to plant fewer acres of soybeans if corn prices are high, or vice versa.
In short, ethanol is not stealing all the sweet corn away from the Jolly Green Giant. I picked up 4 ears for a dollar at the grocery store, and ate them tonight.