Is this a good deal

Im thinking of buying a 95 nissan maxima. The guys says its a temp sensor that is making it run ok one minute and want to die the next. Thats what he was told, but I found 3 temp sensors on autozone an ambient air, a coolant and an egr temp. Which one of these would it be and how would I replace it. This is all going to be considered in what hes asking. Hes asking 800 but its got 200,000 on it. Im thinking 600. Any ideas would be appreciated