Aviation is regulated and you can only figure out the economics AFTER you apply the regulatory restrictions.
Some advertise drones weighing 55 pounds or heavier as more economical. They are when there are no restrictions. 55 pound and heavier drones have two major drawbacks: (1) you are required to stay 500 feet away from people and property you do not own and (2) you are required to stay a certain distance from certain airports on the aeronautical charts unless you have another authorization. This calculator is dealing only with the 500 foot buffer zone requirement.
So what determines whether you should purchase an over 55 or under 55 pound drone?
The environment of the area you plan on spraying!
You are required to stay 500 feet away from any property you do not own. You may have the permission to spray a particular field but do you have the permission of the neighbors? I’m assuming surrounding crops, fences, cows, orchards, buildings, cars on roads are all property you do not own and do not have permission to be around.
The final number represents an approximation and should only be used as a guide. No guarantees or warranties are implied. This calculator is “as is” and you should use it at your own risk.