You know these tight margins are playing havoc with crop budgets and potential profits. The University of Wisconsin has a tool to run various scenarios and calculate your profitability  for the coming year.
The sample uses $4.49 corn  and 181-bushel yield, to predict $402.08 total operating costs per acre (or $2.22/bushel) costs per acre.
Add $123.60 per acre land-ownership costs and other fixed expenses, and Wisconsin Extension gets $3.20 total cost per bushel of corn following soybeans , or $233.12 per acre profit.
Sounds low to me because of the land figure. Plug in your own figures on the right-hand part of the Excel sheet for more meaningful costs.
Thanks to Ken Barnett at the Wisconsin Center for Dairy Profitability for the tool.