For a situation like that (I'm not a pro tree guy by any means, but I do some contract tree work for a guy who has a tree service, and some custom tractor work) I try to figure out a day rate that works well for both parties. You have to know, or at least have a pretty good idea of how much your time needs to be worth. Or you can just take a guess and add a little
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I did some work splitting firewood at a friend's house. Between truck, trailer, tractor, splitter, saws and small tools, I had about $34,000 worth of equipment (what I paid, not necessarily what it'd sell for). I charged him $350/day for me and the machine. I think I averaged 3 hours a day or less on the machine, and only worked 8 hour days. I was happy and he was happy. Assuming you have insurance and some expensive equipment, your cost might be quite a bit higher. Figure out what it costs to keep the lights on, so to speak. In this kind of scenario, you have to add enough to theoretically cover replacing your equipment when the time comes. Then, add however much you want to make on top of that. I imagine there will be a number that is competitive from the homeowner's perspective and also seems appealing to you. If not, well that's okay too.