Hog, when I was still with Cargill, I used to work with farmers and generally tried to steer them away from basing their revenue needs on a per unit or by price. Too many variables. Here is an example:
Had a customer (this was around 2005) who was looking to plant corn under pivot. Not a great well, so usually running around 180 bu. for irrigated.
I made a chart for him, based on historic prices we had records on and his production costs, and wheat followed by double crop milo or beans would have generated more net revenue per acre than growing a corn/bean rotation every single year we looked at. Sometimes the difference was small, sometimes it was huge. He never even considered it, just planted the crop that yielded more and priced at a small premium to milo. He went with a wheat/milo double crop that year and had the best net revenue per acre he ever had, rotated to wheat/bean double crop (and baled the straw) and returned even better.
Hay may be a little different, as you don't have planting costs every year, but with so many fixed costs (machinery, land, depreciation, interest, etc) it is a bit more flexible to establish a cost per acre and see how a change in yield impacts price need for break even. Your cost per unit is a component of the cost per acre. A person may even find that that when running price/yield scenarios, they are looking at the wrong crop