Firstly, you should always have a warning light checked. However, in your case it is a service light that may simply mean the car's comuter has determined it is time for an oil and filter change or inspection. I would drop by your local auto parts store and see if they offer a free diagnostic. Most large ones like AutoZone and NAPA do. If that fails, go to Car Talk’s Mechanics Files site at http://www.cartalk.com/content/mechx/fi
nd.html Enter your zip code and you will get a list of mechanics in your area that other consumers have used and highly recommend. Look for ones that specialize in the make of your car. Call 2-3 of them and ask for a ballpark figure on a diagnostic. I have personally used this site with great success to find good honest mechanics and can highly recommend it. I would only go to the dealer as a last resort. Good luck!