If you are on a new $30,000 tractor that will be considered wore out at 4,000 hours, that alone is $7.5 an hour. Grease, oil, hydraulic fluid, filters, tires are probably around $1000 for every 500 hours (guess) so now you are at $9.50 an hour.
Fuel use is probably 2 gallons per hour? Maybe a bit more? Say $7 an hour?
So now you are at $16.50 an hour. I guess we have not touched on insurance and such. Also opportunity cost of the $30,000 purchase, which is negated by the 0% financing deals but otherwise could be significant.