OMG. I understand that French taxis called usually charge to show up, but Twenty bucks for a two minute drive? The hotel has to do something about this-- it is a mechanized ripoff. The same taxi goes back and forth, the drivers decide who gets what fare, and they extract the maximum from the customers. Could the hotel provide a courtesy car? Oh, they do---- to Paris for 90 Euros. per their sheet. The train fare varies 3E40 or 4E depending on which train you take.
If you possibly can, arrive at the Rive Droit Station and plan to depart by foot from there, wheeled luggage walked about 800 steps back into town. It's quicker and you may avoid an even larger ripoff than I was subjected to: who knows? The concierge may call his brother in LaDefense as the next taxi, and who knows what the meter will read when YOU get in.
I'm not sure what the hotel can do about it, as it is the way things work in France that once your cab receives the call, you've hired it and the meter goes on.