Service 4 wheel drive light on in my 2010 Jeep Grand Cherokee

I doubt it needs a transfer case. It either works or it doesn't. The transfer case is just sprockets an a drive chain and bearings enclosed in a housing. Run away from that dealership. They either don't know what they are talking about, or their looking to making a killing off your pocket book. Sadly there are a lot of places out there like this. What you don't know really costs you. Remember, knowledge is power. I have been a mechanic for years and despise garages like that. Good luck.