If it's really like that, the paint might even buff out nicely without a re-paint. Hopefully the primer area is small.
Did you look closely at the rusty areas too Chuck? Broncos that sit for long periods up in the mountains waiting for snow, then sit for long periods IN the snow when not in use, do tend to rust almost as fast as the ones that get driven.
But if you're in a salty area and it sat more than it drove (which is what it sounds like) your rust might actually be pretty minimal compared to what it could be.
My '71 was rusted through like Swiss cheese in a few places when it was less than five years old. Now, it was driven lots, and already had 60k miles on it when I got it. But five years and rust-through! Crazy what catches moisture on these things.
Since it's a friend's rig, you may have had good access to all these little details. Which is fantastic and even more cool that you have a chance to get it.
I happen to agree with both of the estimated ranges. If it's rougher than you expect, less than $15k for it. If it's as you say, and nothing else rears it's head, then just on bragging rights alone it's worth $20k.
But be aware, even a 20k Bronco is going to need another couple of grand to bring it back to a driveable state. Items that are still "new" because of the low mileage, will still die an early death from old age once you start to drive it.
Things like fuel pumps, rear main seals, power steering if it was ever added, transfer case seals, transmission seals, other engine seals and gaskets, radiators and heater cores if the coolant was not changed at least every five years or so, rubber fuel lines, stuff like that.
The original hard-ish plastic fuel lines may be in perfect shape still, but there were some bad runs that deteriorated over time too, and they tend to fall apart when you mess around with them. Might as well find out now though, as those are small items compared to what a high-mileage vehicle might suffer from.
Good luck. Hope it's as you say.
Oh, and welcome to classicbroncos too by the way!
We definitely love pics of stuff like this. Even crappy Broncos are fun to check out in before-and-after photos. But a real low-mileage model is a rarity as you can imagine.
Paul