There are some useful numbers on the effects of changes in the price of corn and gasoline on inflation in the United States in an article written by one of my colleagues at ICIS.
(Disclosure: I work for ICIS: About ICIS)
cutting to the chase, Al Greenwood says
The study says that the CPI for food rises by 0.6-0.9% for every $1/gal (€0.20/litre) increase in gasoline. The CPI rises 0.3% for every $1/bushel increase in corn