What is a reasonable cost to replae. My (vew)mechanic says $1,000 if I dont and it breaks will become a $5,000 job. Cat has 126K miles makes wjat I thought was lifter noise!

 

It's about $200 to $300 for the cost of chain and tensioner and then you have new gaskets and guide rails so count on another $200 plus oil and filter plus the cost of labour which will involve a few hours. So $1000 does sound reasonable.
Does it rattle all the time and how loud is it?Is the noise comig from teh fornt of teh engine?
If it only rattles on startup and not too loud may want to replace the chain tensioner first which is around $100 incase thats all that is wrong.
If this is not rectified then over time the plastic guide rails will break and the bits will go into your engine oil and if your chain breaks your engine will need serious repairs as the valves will hit the pistons.
So my advice is to get this probelm rectified ASAP>

 

What kind of lifter noise was this? because my 560 is making a ticking noise as well, and most people are saying it's a lifter or a valve. although the noise comes from the other end of the head, not the chain side.