Could be a fair price, depending on condition and location. I live in the Bay Area of California, and everything cost more here, so if that is in a rural area, it is toward the top of what someone might ask for one.
I bought a 2005 not long ago that had 4,250 miles on it. Picked it up in the rain, and so didn't get to study it much or ride it. Took it apart and found all kinds of little things to fix and replace. About $400 bucks worth so far. I also bought HeliBars and a used Ohlins damper set up. So that brings it up to about $4,800.
I would only pay that much if it was nearly perfect, as there could be things to buy. Oh, look hard at the frame. Do a search and it will show you where to look. You will find lots of photos of cracked frames.
I would ask him if it is easy to wheelie. If he grins and says "Oh, hell yes! All the way down the street!" I would get back in the truck, as it may have a bad frame.