Cambelts need to be replaced based on the manufacturers recommendation, usually by mileage or time, which ever comes first. Some vehicles need them replaced every 60,000kms, most at around the 100,000km. While we have the car apart we replace surrounding drivebelts, the water pump, tensioners and usually the oil seals. These other components have done the same mileage as the cambelt, and it more economical to replace at this time than later. Ie if we just did the cambelt and not the other components, we need to take the cambelt off again to fix them. This can usually be done in a day.Prices vary greatly between vehicles.