NP or CP 2.5RS EditionS

What would you pay for a high mileage 2.5RS? http://nh.craigslist.org/cto/4167441153....
I've chatted with the seller about the "top end" rebuild. Claims it has a knocking sound but it starts, runs, and drives. Not sure if he means knock as in detonation, or something more serious like rod knock. Any NASIOC guys know any regular issues that sounds like this? Seems like it could be a good winter beater and ice racer with some work.

http://nh.craigslist.org/cto/4167441153...