Here are cost figures on various farm operations based on cost accounting records of Iowa State University. The information can help you figure out how much field work costs in your area.
Frisby, James C. and Hull, Dale O.
"1965 Costs for Field Work,"
Iowa Farm Science: Vol. 19
, Article 4.
Available at: https://lib.dr.iastate.edu/farmscience/vol19/iss7/4