Out here in Connecticut the chain, tensioner and upper rails run around $450 at an indy and $650 at the dealer. Look here for an excellent discription of the proceedure:
Be sure to have the mechanic check the condition of your cam sprockets as well. My chain has been replaced but my sprockets are getting worn, so I'm planning a four day weekend over the summer to do all new upper and lower sprockets, guides, rails, tensioner and chain. Allot of work but only $450 in parts and worth it to me for the piece of mind.
I've been doing lots of smaller tuneups items with terrific results over the last few weeks. Some easy ones that seem to be 420sel issues: all new fuses (easy and a must!), alternator voltage regulator ($15), Idler Arm Kit ($30), AC Monovalve ($30). New transmission fluid and filter might also be a good idea.
Basically anything rubber or plastic and all your fluids should be suspect in a 15 year old car. That said, I've never had so much fun fixing a car before. They're a real pleasure to work on, you'll love it.