Ryan,
When I was doing tractor work for money, I charged $75 per hour, with a 2 hour minimum. From the moment I arrived, I would start billing. If the job took one half hour, the fee was still $150. However, I would try to find other work on the site to fill the time, if I could.
That was with a 60hp tractor, 8' dual-spindle rotary mower, and a 6' tiller. I worked properties between 1/2 acre, and 20 acres.
I found that it was important to the customers to keep the billing as simple as possible. My competitors had complicated schedules with different rates for travel, load/unloading, etc. I picked up business from this alone. Maybe I didn't make as much as I could have on some small jobs, but I found it more beneficial in the long-run to build relationships with people that would call me back every year. I also picked up business from competitors who wouldn't do anything that they couldn't do from the seat, or that made demands of the customer. If a customer needed extra services like cleaning up a fence line, I would get off of the tractor and pull out my brush cutter.
Some additional lessons that I learned:
Every single customer is different, has a different set of circumstances, values, budget, etc. I picked up business by being flexible and trying to give customers what they wanted.
I did try to educate when appropriate, but I found it important to feel out every customer before offering advice. DO NOT ever try to give pasture advice to an equestrian! Every single one of them is the top expert on equine pasturing. Even when I could identify multiple issues with their pasture ecology and maintenance, I lost every job where I even offered a suggestion.
As others have mentioned, your actual operating cost is probably higher than you think. It's not just the fixed, comsumable, and periodic costs of the tractor. There are also the costs associated with the tow vehicle, fees, taxes, licensing, your wage, and again as others have mentioned, contingency. That last one got me on multiple occasions. I would always scout a jobsite before doing any work, but there is only so much that you can see when you show up and the grass is literally 7' high. I couldn't always keep the bucket low to the ground to block obstacles because on some properties it would lay the grass over and it wouldn't get cut. Sometimes I hit stuff. I backed my new mower into a boulder that was all but invisible in a blackberry patch. I forgot that I hadn't burned off and adjusted the slip clutch. That was expensive. The owner didn't know it was there. I hit a hidden boulder one day when tilling a garden in a large suburban back yard. That setup didn't have a slip clutch and the shear pin didn't break as it should have. The tiller bounced about 8" up in the air and came back down on the rock, breaking several tines. I always carried spares, but not that many. I was shut down until I could get replacements from the dealer a few days later. That meant another trip out to the jobsite. Again, the customer didn't know it was there. Sometimes it's less serious, like spooling up 200' of fence wire that was hidden in the grass I was mowing. It took about three seconds. It didn't do any damage, but it takes a lot of time to cut and unwind all of that. One day I hit a pile of buried metal junk. An 8" long piece of shrapnel embedded itself in the sidewall of one of my rear tires. I was out $800 for the tire and another $400 for
ballast. It took the rest of that day just to get the crippled machine back onto my trailer. I lost that whole week of billable time while I waited for a new tire to arrive. The point is, unexpected things WILL happen even when you do your diligence and use best practices. Expect the unexpected, and expect it to be expensive.
You won't be able to please everyone, even when you do everything that you can.
To answer your specific question on billing, that's a tough one. For me, every property was different. There is a wide variety in the geology here. Through experience I was able to estimate that I could till about 1/2 acre per hour, at 3 passes and 6" deep. However the actual time varied quite a bit. That was just an average that I learned by looking at records from a year or more of tilling jobs. I rarely found it useful to try to estimate based on ground speed.
Lastly, I probably don't need to mention it, but it's really coming back to me now - Remember to enjoy the good times. Not every job will be easy or fun, but some will be. I miss some of those hours in the seat, listening to the growl of the diesel, the hum of the gears, and the swishing of the mower blades through the tall field grass.
The biggest take-away for me was that good, old fashioned customer service was actually more important than having a competitive rate.
I hope that helps and is not too verbose.
