What is the cost to replace timing chain for 2003 nissan sentra gxe? When i should change it. It completed 95000 miles. What other things i should replace or inspect when go for service?

Probably pretty expensive considering all the parts that have to be removed to do the job. You really should not need to replace the timing chain unless you have a problem with it. I am assuming this car has a ka24 engine and to replace the timing chain the valve cover timing covers and oil pan need to be removed. If you have never replaced your spark plugs its probably time to do so. check the belts and filters and you should be good.