My 1991 Camry 4 cylinder has the water pump driven by the timing chain. I assume that is why the talk about changing the pump at the same time. I took my camry to a mechanic I trust and he hapened to have one on the lift with the covers off and showed me the pump. He said he would only charge me what the pump cost as the labor was almost nothing while changing the belt. I agree that if they want to charge you the same for the pump and again for the belt, I would just wait a week and take it back to have the pump changed.
Someone said why change the pump if it is not leaking, to that I say why change the belt if it is not broken... Just spend big bucks later.