I spent many hours determining pricing earlier this summer. Although mine was not specifically for overseeding, I would approach it the same way by changing a few lines in the spreadsheets I came up with.
No matter how you do it, you have to start with some assumption or standard. I began with the notion that there had to be some minimum size property I would work on and I wanted to arrive at some minimum charge covering that (or anything smaller). That included the time and trouble of getting all necessary equipment to the job (and back), the time I expected the actual work to take, and some return on the cost of the equipment. I wanted to know that number and to then determine what additional units - either per acre or per 1,000 square feet - would require.
From there, I experimented with variables such as my time, equipment time and what that might be worth, fuel consumption, a profit & overhead figure, materials, etc. In determining my minimum as well as my "additional units" pricing, I distinguished between technician time and general labor time to reflect that I work alone. Larger companies might provide labor requiring varying degrees of skill using different workers. For instance, I used one price per hour for figuring loading the equipment on the trailer and moving it and a higher price for pesticide applications once at the job site. For pesticides, I have a “no exceptions” fee for filling out the paperwork since the inspector allows no exceptions. Really, this has turned out to be a great tool for me and good information for the customer.
The materials you expect to use are, of course, an important variable and often one of the easier ones to determine. You have to decide for yourself how far you want to break things down. Whatever you do not wish to itemize (internally, not for the customer) needs to be accounted for in your overhead number. In my case, an example is my trailer; it’s just something I have with me, I made to attempt to determine what pulling it around costs me or is worth. The time spent loading and unloading it was broken out in my pricing model.
I have never understood how the "two times normal rate" approach could work well. On this board, I see it mentioned often with regard to sprayed fertilizer rates and mowing rates. It must work for some people. I am not criticizing it, I just do not understand how it plays in determining equitable pricing. It seems like if you had a tremendous amount of volume it might save a lot of time spent on estimating, but it also seems like shooting in the dark. The real pricing question I was trying to answer for myself is: what is fair and affordable to the customer and is also worthwhile to me? We are all alike in that I am sure.
Good luck with whatever approach you decide to use. Mine is a work in progress to be sure.