OM603 timing chain job

My girl's got 260K and I heard what I think is timing chain slap. I want to roll a new chain in there..

First of all, how would one go about checking the stretch, and what is acceptable?

Second, how would one go about rolling in a new chain? Do I need a chain crimper?

Is this best left up to a compitent mechanic, and what would be a fair price for a new chain?

Thanks!