yes, they are at/over $100 per key and they will have to be reprogrammed.
Go to this link below, this forum member has a similar car, and just went through a no key situation, which he recently fixed.I purchased a MBZ 1997 S500 Couple, that is in very good condition and it runs great. However, it only came with one key and I'm worried that I will be stuck if I can't get another one made. I've checked with several dealers in my area as well as contacted the corporate offices of BMZ and I was told that Mercedez not longer supports the keys for this model as well as any other model that uses the Drive Authorization System. I also reached out to a place in Great Britan that claim they were able to create replacement keys for these cars but I needed to bring the car to them. So now I'm reaching out to anyone in the US that has access or the ability to make me a new key for my car.