SeanJohn,
Whitey knows his stuff ! Yep, $15-20K for a decent unrestored truck--but what is that? While they may ask for that much or more, my opinion is that would be a high valuation for most of the South/Central American 40/45/47 series that are first sent here. Yes, a very few companies can do fairly nice to very-nice restos, but those trucks won't be for sale at that price. In that part of the world, these vehicles are used as mules and pieced back together with whatever's available to keep 'em working. North Americans are seen as gullible and easily fooled. You've already seen the non-stock bed, the front lamps, likely some odd switch gear, and a nest of black-taped wires under the dash.
Take a camera and an ice pick with you on your next visit and check the soundness of the frame; look for tarred-over welds, rot in the floor pans, rockers, and door bottoms. Do a righteous comparison with your own 40 series. You may see genuine leather--not OE-- but be on the lookout for a quick slathering of Bondo and a hasty coat of lipstick on a worn-out work horse. You can politely listen to the story of how it was used sparingly by a little old lady from Cartagena who only drove it to church on sunny Sunday afternoons, a nice story, but verify that matches what you're seeing as you spend time checking it out.
Don't want to kill your dream or your enthusiasm, just be smart about carefully evaluating what you're getting and what more it will take to make it what you want. Good luck !