It's going to depend on the location and condition. $13K doesn't sound too far off for what these trucks are bringing.
The engine at that mileage may need some freshening up such as injector O rings and the such but if it run, no smoke, and starts up right off of the bat it should be fine.
Odds are it is a automatic so that would be the big question is what kind of shape it is in, a 6 speed will bring a premium price. Also if it is a 4x4 will keep the price up there, if it is just a 2 wheel drive then it may be a couple thousand too high.
If you to to Kelly Blue Book I would wager that they put it into the $6000 price range but they are low on the 7.3 engines.
I recently talked with a person who works at a local auto auction. He said a truck like mine, see signature, would go for about $14,500. This was without him being aware of the BTS transmission and oversize fuel tank. However, my truck has no rust or dings and has been garage kept the majority of the time since I bought it new. I was quite surprised at his valuation.
I’ve been offered 20k for mine plenty of times and I’m not selling. It’s funny that my neighbors 02 blue books for 17k and my 03 shows 6k but they never let you pick the 7.3. Just assumes it’s a 6.0 I guess.