As far as routine parts in maintenance are concerned, they are easily available, like plugs, coolant, lubricants, filters, etc. Yes, body parts of Mercedes are expensive, but then genuine, OEM parts of Toyota and Honda aren't cheap either.
Main issue is, Mercedes k case mein "thukk thakri" ya "khainch taan k" kaam nai chalaya ja sakta, like Japanese brands, etc. If it requires timely maintenance, or parts replacement, then it mean it.