That's a hard question to answer, there are a few mods that are recommended by everybody who has them and it's hard to put a price on a truck that is not right in front of your eyes.
But I would not sell my M880 for less than.
1) Complete with troop seats, cargo cover and blackout lights : $6,000.
2) Just the truck : $5,000
That being said, I have seen good prospects for restoration going for $1,500.
( just the truck ) And paid $2,300 for my unit in '06 complete but un-restored...