It is around $7-8 per acre for custom guys around us.
I like your concept of by the hour if the field is rough. Rough fields are too hard on equipment that is expensive to replace, and the per acre rate not really appropriate in that situation. Sometimes you don't know until you get to the field that it is rough.I don't know what area you are referring to but I charge $6 for 5GPA, $7 for 10GPA, $8 for 15 GPA. That is for where I am with mostly decent size fields and relatively flat. Small, cut up fields with lots of obstacles expect tp p[ay MUCH more in some cases. We charge by the acre (because that is easy for the customer to understand) but it is REALLY calculated by the hour. If a field is unreasonably rough I won't even spray it but if I am already loaded before I see the field, then I charge by the hour ($24 per minute starting when I kick on the booms and stopping when the field is finished). I have not had to do this for quite a few years as I TRY not to spray outside of my regular customers and they are real farmers so no situations like that.
A local farmer used to do custom spraying. He was hired to spray a field that he was told was not too rough. He loaded the sprayer with roundup in the yard and went to the field to find is was plowed. He stopped cracked the valve and dumped the load in the ditch, loaded up his sprayer and went home. I USED to not uncharge for rough ground and hitting a rough field` would make me VERY cranky. Then I started to charge by the minute and took my time. You era right, just charging my "normal hourly rate" does account of the added wear and tear so I go REAL slow. Haven't had that issue for many years now.I like your concept of by the hour if the field is rough. Rough fields are too hard on equipment that is expensive to replace, and the per acre rate not really appropriate in that situation. Sometimes you don't know until you get to the field that it is rough.
Pretty sure that a ground rig costs more than an air tractor to purchase but not as much to operate.I wonder about the narrowing of rates between ground vs air rigs - I think gap between the cost of a new ground sprayer and an air tractor has narrowed substantially in the past couple years.