you need to sit down and have a offer-counteroffer session with him. offer BB, see what he says.
you should also look into what has been done to this car. is it a turbo or not? [is one of the gauges a boost gauge?] has it been raced to hell and back? obliviously somebody was racing it around. and here you are already complaining about the exhaust, and if it has a cat on it it can't be THAT loud...