The water pump for a car or truck or other vehicle is pretty cheap but what costs the most is the shop labor to remove the old water pump and replace it with a new one.
You have to drain the coolant, remove hoses, remove belts and possibly some other things to get to the water pump and then you have put all that back together again which take almost a whole entire day or can take the whole day to do the job.
The water pump usually costs from $15.00 to $200.00 depending on the make and model of vehicle and then the labor can cost around $200.00 to $600.00 depending on the vehicle.