I am an independent, well experienced CFII MEI doing only PT and I charge $75/hr cash. If the PUI is late, they still pay. I give them my all, every minute we are scheduled, and expect the same from them. I don't charge for my time on the lunch break for a XC or anything like that, as long as they don't lollygag. But if they are making phone calls, wasting time making a video or whatever....I'm waiting on them, its my time, so I charge. Some go elsewhere, but I find that the ones that stay with me are serious flyers and don't seem to mind it.
I also know a cpl who charge close to $100 an hour but they are strictly flying with the doctor, lawyer, Indian chief types.