I've been riding GS500 since last August, very good experience. One important thing about buying a GS500 in Pakistan is to make sure that it is restored in a proper way. Many people just restore it with ordinary/faulty parts to sell for profit as this bike has always been in demand.
As for budget is concerned, these days an immaculate condition GS500 will in no case be less than 200k. The days of 100K and 130k are gone as ordinary bikes like Deluxe have got so costly and the inflation+increased new bike prices have made it a costly game.
GS500 is allowed on M2, in fact a friend is getting all the required info in this regard as we both plan to take our bikes to M2 together. Will update in this regard once I get some info from his side.