It appears to be aearly to mid 1980s model that has been upgraded with a new rear derailleur. Normally this would be part of an index upgrade but the shift kevers appear to be friction models. It's hard to tell from the picture but it is possible that some the other components are early 1980s 600EX.

As suggestred you need to obtain particulars on the other major components and the tubing decal.

KHS offered a full range of bicycles from entry level to professional level racers. They were a reutable brand offering good value at the various price polints. Unless the asking price is outrageous, it would be worth a closer look.