It is usually recommended to replace the chain between 80k miles and 150k miles, depending on the engine type and the way the car has been driven. Chains usually only jump teeth or break at high rpm's or sudden violent accelerations.
In your case I would say the 100k mark sound good for some preventative maintenance.
Parts are inexpensive. You'll need the chain, master link(usually comes with the chain, tensioner, inner and outer rails and the clamping lever.
The labor is another thing. I do the work on mine myself so no cost for me there. Get a quote on the labor form a reputable mechanic and say you'll provide the parts. Always make sure you collect the "replaced" parts though and that they are the ones from your car.
P.S.:Feels great the be cruising in a Benz as a student,hm?!
Been there, and I liked it a lot.