The vibe I get is that he probably isn't going to be a motivated seller.. giving up the truck is esencially closing a chapter of his life.. and sometimes thats hard for folks to do.
What the fair market value for the truck is, what you can afford to pay, and what the owner thinks it is worth are often three totally different things.
It's just as easy to point out other folks who've paid $300 for a simular truck as it is those who've paid $10,000.. you'll always have instances on extreme sides of the scale.
Forget bluebook and other sale prices.. sit down, figure out how much the truck is worth to YOU, and shoot him a price thats a shade lower than that figure (that way you have some wiggle room if he counter offers)
That's the way I buy stuff.. I calculate what I think the thing is worth to ME.. if the seller wants more, then I wish him the best of luck and go on my way.