by AMG i take it you mean the 2.3-16v (AKA - "cosworth"), this means it's one of around 5000 cars ever made. now if it is an original i should point out that it is a very desirable car, but it MUST be maintained from teh factory adn must be running at 100% at all times. cutting corners on work on such cars means that they are being ruined by the owner.
if the car is not shahnawaz maintained then i'd suggest you walk away as it'll cost you another 8.5 lacks to get it back up to spec. old mercs are not cheap to fix but these cars have a speciality deler & parts network in the US and europe so you'll probably be able to source all the parts you'll ever need for it.
if it is a good clean car then 8.5 is good value for money (considering the garbage available in PK in that price range).
good luck and share some pics.