How much would it cost to install a water pump?

You can get that estimate here www.repairpal.com/estimator and find a shop here www.repairpal.com/directory

$600 to $700. Apparently they have to do a lot of dissassembly to get to the pump. I wouldn't wait too long to get this taken care of. If it's the bearings and they let go, the fan could come off and do considerable damage to your radiator and other components.