When calculating "cost" or "profit" from bush hogging (or ANY tractor chores) be sure to consider replacement of equipment somewhere down the line. You can pay for fuel, cover the obvious cost, make a few pesos for yourself, and MAYBE even pay for insurance. But 10 years down the road, when that tractor is worn out, have you made enough to cover repairs or replacement.
I've owned a tractor or three at any point in my life since leaving high school. There's always someone wanting a field mowed, or a garden plowed. I used to jump at the chance. After adding 150 or 200 hours a year on a favorite tractor for 10 years in a row, I began to realize that these people need to be paying more for my services.
IF... I can get what I want, I'll do some side work. But in general, they can usually find someone else to do it cheaper.
I'd stay upwards of $60 for any tractor. Bigger, higher horsepower (heavy fuel users) go upwards from there.
Just yesterday, I priced mowing 25 acres of pasture to someone. Last year, that would have figured up to something like $400 to $450. This year, they'll be paying $600(+) or I'm not their guy. (And yes, I got the job I priced out,.....$600. About 7 hrs counting hauling time)