i'd offer the guy $3500 tops. it appears to me from those pics that the bike sees mostly highway and wheelies seeing that it has a cage, 56 tooth rear (stock is 43T), bigger chicken strips than raisin canes, and some damage. the fork seals are probably shot and its going to cost you about 500 to get that back to a more streetable setup (rebuilt forks, paint on that side fairing, and stock gearing).