Assuming you don't have a 3.3 or 3.8L with a timing chain....
flybyy has it correct. It involves quite a bit of labor to change a timing belt. You have to remove a lot of items to get in done. That's important to understand, because you will be faced with the decision to look at the water pump, and even possibly cam seals while your in there.
The parts themselves are relatively inexpensive, but it takes a substantial amount of time to complete the task. At 83k your probably at a good point to consider changing it.
If its out of warranty, my preference would be to take it to a local shop that you are familar with or do it yourself. Some people go to the dealer no matter what, and its a personal thing. We've seen time and time again, that even for simple jobs (like brakes) the dealer's seem to charge extraordinary prices. In some instances they are cheaper, and many times they are cheaper for parts. In the end, take it where YOU feel most comfortable that the work will be performed properly, efficiently, and at a price you can live with. Shop around and get a good feel for 'typical' prices in your neighborhood, then go with your instincts.
Oh... and I would be changing the water pump & its o-ring while you're in there.. its cheap insurance. The water pump is driven by the timing belt. I doubt you'll find a mechanic who wouldn't recommend it to you, unless its been done recently.
My 2.5 cents.