mid-late 1980s S-Class V8- good price for chain replacements? (87 420SEL)

[86560SEL]

Can anyone tell me what a fair price would be for a timing chain replacement for a 1987 420SEL, as well as a 1985 500SEL? I am considering to purchase one of these and wanting to know what the maximum I should pay for a chain replacement on these cars. The 87 has 178K (priced $2900 OBO) and the 85 has 152K (priced $5200). Not sure when the chain was replaced on either, so it may be best that I have them changed. Is anyone cheaper than the other? Thanks!