You can look at costs of tillage to smooth out ruts and lost production due to compaction. We might assume an extra pass of disk/chiseling at $15/A (see http://www.extension.iastate.edu/agdm/crops/pdf/a3-10.pdf).

So if 25% of a field were rutted and production in those areas reduced by 10%; that would mean a 2.5% yield loss. At 200 bu/A and corn at $6/bu that would be $30 lost/A.

So perhaps $50 cost per acre for rutting is not unrealistic.