There is a wide range of cost depending on the vehicle.
On some cars there is a choice of replacing just the timing belt instead of replacing, with the timing belt, the water pump, belts and hoses (as needed), pulleys and tensioners (as needed) and possibly a few other maintenance parts.
Even though replacing just the timing belt saves a lot of money, don’t be fooled. If you like the car, and are planning to keep it as long as possible, do the complete job!
Some are quick and simple (Subaru, some for Honda and for Toyota) some are a real pain in the ass and expensive (for VW with the W10 or old GM 3.4L DOHC). There are other things that add to the cost (leaking cam seals, tensioner, water pump, and pulleys) .So the most honest answer I can give $250-$3000 (VW Phaeton on that high end was the most expensive I have ever seen). Go by recommended interval.
Looking forward to working with you
Mainly producing timing belts,air filters,oil filters.