In a recent game I was in the party was walking around with something like 70,000gp in Diamond Notes (the Shadow World solution to mass currency transport). Depending on how you value a Gold Piece* that is the modern equivelant of between £8.3M and £350M ($13M – $539M) in cash. That was the cash surplus after four months of adventuring and treasure hoarding.
The first question is how much money do adventurers actualy need? They could retire quite happily and live out a life of luxury on that sort of money but then they would not be adventurers if they did that sort of thing. As a GM it sometimes becomes necessary to drain money from the players economy. One way is the herbalism method.