I will say though that the first truck really isn't that rusty. Sure, the shocks, ABS wires and some of the bolts are pretty corroded, but those are replaceable parts. The frame still has all the paint on it from what I can see and the parts that they took pics of appear to be the rustiest parts. See that inner bolt on the rear crossmember? That one looks normal. I think a few hours underneath with the angle grinder and a wire wheel, followed by repeated applications of either Fluid Film or bar chain oil would make that rig pretty easy to work on and the rust is totally manageable if you keep after it.
I realize that it is more work, but dealing with a rusty truck really isn't that bad if you have patience. Sure, rust free is better, but if I am buying something to use and drive I would rather buy the slightly rusty truck that I can look over and see in person than take a flyer on the kinda beat looking FJ80 that has at least a handful of significant issues visible in the few pics they shared.
What does the body on the rusty one look like? I can deal with a rusty undercarriage, but I am much more averse to rust on the body in large amounts.
All that said, I wouldn't pay $6000 for either one of those rigs. If the rusty one was running good and the interior was decent and the body was solid, I would pay $3000-$4000 for that one and I don't think I would go past $4000 for the 3FE one.
If you really want turn key, really good overall condition, I think you are going to need to think about spending more like $9000-12,000 if you also include the inevitable new parts it will need, shipping, taxes, etc. That's just pretty much how much those cost these days. Sure, people will say that they got their triple locked beauty with manual cloth seats, no running boards, no sunroof, no roof rack, with all PM done for $3000, but those people either really lucked out or they don't understand where the market is for these trucks is right now.
The bottom line is that these trucks are rare and sought after. There are very few left that are owned by the original soccer mom that has no idea what it is and their prices reflect that.
If you want to get into a reliable 80 Series you either pay up front or you pay by fixing one up.
If you aren't in a rush and you want rust free, you'll have to be willing to travel or pay to have it shipped. The best cars are from the Pacific Northwest where it rains but doesn't snow a ton, Texas, Southern California, the desert southwest and then in the urban southeast in that order. Anything from the mountains will likely be used heavily and anywhere right next to the ocean is prone to have rust issues. Trucks from the desert and high heat areas will have more paint and interior issues and all the dust and heat does a number on the rubber under the hood and in the motor itself. The midwest is OK if you can find something from OK, MO, KS, the Dakotas, etc that didn't see a lot of salt, but they weren't popular cars there. Everything from the Upper Midwest or the North East will be rusty AF unless it was one like mine that was stored during the winters for the most part.
Honestly, I see some of the best deals on the trucks that have been maintained the best right here in our classifieds. They aren't cheap, but you have a much better idea of what you are getting.