There is no real answer to this question, all pricing depends on the area where you are working and what people well pay for the services. Some charge by the inch, some by the hour. I figure jobs both ways to come up with my final price for the job. When I started in the business I called a couple rental stores and found out what they charged to rent a hydraulic grinder for a day. I took that price and divided it by 8 and figured that was the minimum I needed to make for my machine per hour. Added what I felt I should make per hour and added the costs of insurance , truck, saws etc and came up with a minimum hourly rate.
After doing a few jobs and losing money, I'm now able to figure how long a job is going to take. By measuring the stumps and using an average competitive price for my area, (It can be differcult to find out how much others are charging, but it can be done) and figuring how long the job is going to take to do, I now make a few dollars and can be competitive with the other companies.