the tech at the dealer (where I go for major jobs) gave me an estimate of 1 hour labor for just the tensioner, and 3 hours labor for tensioner plus chain. For tensioner plus chain plus upper guides, he said about 5-6 hours labor. Its an 85 190E 2.3 - I have 125K, and am planning to get at least the chain and tensioner replaced - I also have a bit of a clatter on cold start. About the upper guides, he said it was not a problem area in the 190E's, at least till 200K, so I might hold off on that.
Meanwhile, be sure to change your oil more frequently than ever, maybe at 2.5K.