I get asked to do "simple" or small grading tasks and you have to set a floor of prices or you'll be in a fools errand and be asked to do lots more small time wasters and money losers by countless others who wouldn't do the same for you.
In my biz, you aren't just taking an implement with you but hauling an expensive vehicle and trailer that requires insurance, fuel, depreciation and inherent liability for an accident on the way. You could damage a tree or make a rut in the yard. .
There is what's stated to be done but there will be unspoken prep work like getting things ready to do the job or stuff in the way or do this "while you're here" such as another small leveling or "hit this with your seeder". Plus job liability in that anything that goes wrong the owner will fully expect to be made whole at retail prices at a minimum. Scrape a 15 ft tree in a small way and the friend will want a new one R and R'd by another guy that sells trees and charges top dollar.
Long ago I waited 20 minutes for a guy to finish a cell phone call while I did him a favor. Another was a struggle collecting even a pittance fee.
No thanks to all of that because there's a line around the block of others wanting the same waste of your time.
If I do a job requiring a an implement with me, I charge $150-$175 for the first hour and then $125 to $150 an hour after. Plus materials used. For those who ask about small jobs I state the price right away and say it's too expensive and to do it yourself. That's actually the answer they expect. This has kept me out of the fray of sliding downhill and oddly enough, people that pay these amounts often want other much larger things done. Plus they give referrals that are pre-qualified since the people know the price, know the workmanship and know it's a business and not a help your friend effort.