That is exactly why I dont price by the hour. And the people that charge by the hour, usually arent getting as much business.
Skill level and equipment have a lot to do with it and not just the size of the cutter.
I have a 5 footer on my
L3400 and I can assure you that I can be more productive (especially if obsticals or difficult terrain) than if I were to use the same cutter on dads 8n (which a lot of the adds around here state something like "8n and 5' bushhog for hire @ $40 per hour".
8n lacks live hydraulics, doesnt have a live PTO, and no shuttle shifter, and not as much HP. I can outwork an 8n. But If I were on the 8n and a newbie city slicker that has never ran a tractor is on one like mine, I doubt he will be as productive either. So skill level is important too but that is something the customer doesn't know going in.
All reasons why I quote by the job. But in the back of my mind I am figuring how long it will take me and measuring how many acres there are. It is a good Idea to get one of those rolling measuring wheels and take a calculator with you when you bid a job. 43,560 sq ft per acre.