According to the USDA-ERS Food Dollar Series, “For every dollar spent in 2016 in the U.S. on domestically produced food (food dollar), U.S. farmers sold 14.8 cents of farm products to non-farm establishments (farm share), down from 15.5 cents in 2015. The farm share is at its lowest recorded level between the years 1993 and 2016.”

Some additional points of interest include:

Farm production costs per food dollar fell to 7.8 cents in 2016 and are at their lowest level since 2002.
Foodservice costs per food dollar rose in 2016 to 36.3 cents, increasing for the 8th consecutive year since 2008; foodservice costs were 29.0 cents in 2008.
U.S. worker salary and benefits increased from the previous year, accounting for 50.6 cents of each food dollar in 2016.

The farmer share of the food dollar measures proceeds of farm commodity sales tied to a food dollar expenditure and sold to non-farm establishments.

You can find a lot more information including an application here that allows you to search and download data.