Supply and demand as well ascost factors pretty much determine local going rates for custom work. Sometimes, however, there hasn't been a rate established. In such cases, this guide may be of help.
Armstrong, Ray E.
"Iowa Farm Custom Rate Guide for 1962,"
Iowa Farm Science: Vol. 16
, Article 3.
Available at: https://lib.dr.iastate.edu/farmscience/vol16/iss7/3