He's probably spending as much, if not more, on gas for the rental car than what a hotel room would cost. Doesn't make any sense, unless he's paying you two by the day - then he's just being cheap. He could at least airline you home.
On long overnights like that, we have the option of staying or airlining home. The cost is pretty close to the same either way, usually. We're on salary, so that isn't a factor.
I've been pretty lucky my whole flying career that I don't have many horror stories. Back when I flew 135 corporate charter, I had a few goofy passengers, and I flew with a goofy pilot or two (or three), but in general it's all been good.