I've been looking for a cleaner pickup for a year now and I just found out that a relative that lives about a days drive from me is hanging up his license. He owns a garage kept 2003 Ford Diesel Supercab 4x4 XLT with an automatic trans that has 18,400 miles on it. Its been his baby since new but he lost the ability to drive soon after he bought the truck. Its been sitting in the garage ever since. He calls the Ford dealer when it needs service or new batteries but its not been driven since 2005. It does have 6 new Michelin tires on it, two new batteries and all new filters.
He told me to make him a an offer. He's family, so I want to be fair.
NADA calls it $16,500 but it gives the same price regardless of mileage for that year for some reason. Those like it that I see for sale around here are listed at $22 to $24k, but those are big dealers.
Can anyone give me any insight as to what something like this should be worth? If it was yours, what would you ask?

I'm also a bit leery of the 6.0L Power Stroke, but it runs fine and I doubt I'll put enough miles on it to ever need to worry about the issues people seem to be having with it. Especially in a stock vehicle. I'd only drive such a truck maybe a few thousand miles each year so the thing would likely out live me sitting in my garage here.