Picking which price to use could easily vary another 10x either way. Is the government using local farmer's markets, retail at grocery stores across the country

Picking which price to use could easily vary another 10x either way. Is the government using local farmer's markets, retail at grocery stores across the country, or the price that retailers pay farmers? What does a "bulk" price mean for grains? Corn is at about 7 cents per pound, if you buy it a metric ton at a time on the commodity market. Not saying the result you got is necessarily wrong, but I'm very skeptical of economic comparisons that don't carefully control for these sorts of things.