Within the script, I would look to see how much is being charged for each commodity and change it to suit your server. This is a nice gold sink and also I am sure the players will be more than happy to pay the price if available.
I got it to take gold from the backpack or the bank box. Most of the time the cost is high enough it is coming out of the bank.
I set these up on the Floating Emporium, where the cranes and scaffolding are located to look as though goods have been off loaded by the Merchant Galleons.
TODO: I wanted to have a message on there when you purchase the goods, so you know the money was removed from your backpack or your bank account, but I could not get that part to work. Any assistance on this is greatly welcome!