I have never been a huge fan of the caddy swap and have seen some of them done in such a way that I feel my spine snapping from an accident just by looking at it. Extending the bed also brings up some issues with frame construction to add the extra 3 feet.
And also the shave job on the doors is probably ok but I have seen countless customs that have had wiring issues with the poppers.
If it was all done right and the body work has been done right, he has easily 10 k in bodywork alone, be it his time or a shops, plus the suspension work is probably another grand. And I'm
Betting there is probably some interior work so well say its probably another grand. Plus the truck itself is probably worth 6 or so. So total value of the truck is probably right around 20k if it was all done correctly and is finished. If he is handing you a project it would be significantly less. And not to knock your ranger but I wouldn't put it close to that maybe 10 tops.
So I would be very suspicious of this trade and would look for some indication of a mechanical problem.
If its something your really interested in the trade go over it with a fine tooth comb. Check all panels, wiring, the welds on the frame, all the work that has been done to bring it to where it is now.