Did the bolts come loose, or the pulley itself crack and fail? If the pulley failed, about all you need is a new pulley, and belt. That would be relatively inexpensive, 100 to 200 I would estimate. If the bolts came loose, more than likely the water pump hub is damaged. Therefore, the pump would need replaced as well as pulley, and belt. You could be looking at 300 to 500 approximately.