Yes, very expensive. I try to have a local locksmith to make me one and he started cursing saying that Mercedes charge then more than $5000.00 to sell the software to other locksmiths and also Mercedes requires then to update the software every year.
He was so anger that he told me: "if people have the money, $52K to buy this car, go to the dealer and pay then to make a new key, do not come to me"
The price varies a little bit from dealer to dealer.

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Nyck - TX - USA