See below the dummy reservation for a hotel in New York. This is also a "Name your price" so, "supposedly" priceline does not know which hotel will be picked (which I find hard to belive).
So here they DO state the hotel fee.

How does that sit with your explanation? So, in some cases they state the fees, and in some it is vague "possible amount". The customer is entering the contract when the full and exact details are not disclosed.