The cost of the parts to replace a timing belt and water pump range between $50.00 to $80.00 and sometimes as much as $150.00 depending on make and model of car.
If you buy the parts online and then do the job yourself you can do the job cheaper.
But when replacing the timing belt you must make sure you get the engine timing correct or the engine will not run properly or at all.
Make sure the timing marks are correct otherwise the engine will fail to start or at least start but run rough.
If you hire a shop to replace the timing belt and water pump the cost could be between $200.00 to $900.00 and even sometimes as much as $1,000.00 depending on the vehicle and how hard it is to get to the timing belt and water pump.
It also depends on the shops rates for labor and if the shop uses their parts there will likely be a markup as well.