How much to roll in a new timing chain?

I was wondering how much it will cost me to have a new timing chain rolled in on my '83 300D? How often is it recommended that this be done? I have read a lot about just checking chain stretch, but aren't you still risking the chain snapping unexpectedly after a certain number of miles? I have heard of mercedes with over 200K on the original chain, and some with a wrecked motor after a chain snapped at 115k - opinions? Also, can I do this myself. I'm knowledgable enough, but I know to change a Saab chain you need all kinds of special tools - what is needed to roll in a new chain on a 300D? Thanks

Greg