Although it is one of the more costly repairs, replacing a timing belt is far less expensive than the "alternative".
Timing belt replacement times vary by manufacturer and model of vehicle. Consult your vehicle's owner's manual to determine the recommended service interval. If a timing belt should fail, the damage to the engine is irreversible.
As you're replacing your timing belt, it is recommended to also replace the water pump, oil seals, tensioner and pulleys. Performing all of these repairs simultaneously is recommended because most of the labor to change these parts is included with the timing belt change, instead of paying the same labor each time one of these parts fail.
Timing belt replacement is a complicated job. Don't trust this job to anyone else but one of our ASE Certified technicians. Engine damage from a failed timing belt could be irreversible!