Unlike chains timing belts do not rattle when they are worn out. They just break when its time. And it's anybody's good guess as far as when a rubber (timing belts are reinforced rubber belts) is going to snap. Good rule of thumb is to replace it at about 80000 miles. If you look at the mechanism idlers/tensioners and often water pump is a part of it. It's like you have to take off your shoes before you can get into socks. So if someone tells you that all that extra charge is for everything else and not just timing belt then may be it's time to call it bs and use this latest technology called "INTERNET /GOOGLE".

Mind it that timing belt synchronizes the valves with piston and when it breaks it causes the piston to hit the valves and thus you can take your engine to funeral after that, unless it's a clearance type..mostly in Toyotas.

And like a few people indicated timing belts are cheap..could be as low as 25$ in AutoZone with 2 years warranty. Coolant pumps often come with lifetime replacement warranty and will probably cost 50 to 100$.. Tensioners/idlers may be 20$.. And btw it's a good idea to replace other serpentine belts at the same time because they have to be removed before you can reach timing belt( cant take off socks with shoes on).

Hope that helps and good luck. And btw changing a timing belt isnt all that difficult if you are patient though it looks intimidating at first glance.