Hard to say Phil. I personally think it would have to be an exceptional amount.
Maybe a stupid example but regulars of ours go to one airport where parking landing etc overnight is around £850. Has been suggested they go 25 miles away where it would be £150 but they won't hear of it.
On your first point charging for hotels and taxis is a poor show I think. Especially as most FBO's also earn commission from said hotels and car companies. I haven't yet been charged for this. Yet! Same with say dishwashers. Surely it should be part of the service.