I don't know if I have answers, but I do want to ask you questions:

What do you want to know?  Do you want to know what that IH784 is costing you on a yearly basis?  Or do you want to know what your equipment costs overall?

I think many dairy farmers that I know would want to have break down by crop- corn, hay, soybean, small grain, etc - but not by specific tractor, etc.   I think dairy farmers would want to know cost of harvesting, on a per acres or per ton basis..

If you want to know what specific tractor, etc is costing you might want to keep a separate log page for each one, and just track when maintenance was done on that equipment, and date completed, and hours if you have them.  This can be as easy as 3 columns on a page:  date;  repair or maintenance completed; hours on equipment.  You could look back thru a log and determined if the equipment has too much time in the shop.  However, I would not keep this in your overall financial budget.