Acquisition cost, fuel, repairs, registration, insurance,(not typical but I like to include the cost of buying a new machine...I.E. If I will get 15k hours out of this machine and a new one is $150k therefore you will need to include that $10 per hour to get to the $150k for the new machine.) There are some more do not recall them all divided by the anticipated hours that you will use it per year and then your got you hourly cost. An excellent book to give you better guidance on this is Jim Huston: How to Price Landscape and Irrigation Projects. Yeah seems off topic but the book teaches you how to cover your costs across the board. Jim also consults with tree companies, he is a great guy and knows his stuff about the industry, definitely something to look into.