I'll add to this good list and other comments to date it's October 2020 as of the time of this post and all these trucks are over 30 years old now and unless they've been in a climate controlled Barrett-Jackson Garage for decades you're not going to find a cheap K5 that does not need one of just about everything...
How soon one of everything needs to be replaced is the question and how much of that can you do yourself...
A 100% Rust Free K5 is a Unicorn even in the southwest...
Just about any K5 you find that has not been restored is on it's 3rd or 4th Engine and Tranny by now, speedometer has probably been turned over 3-4 times and or replaced, on these K5's stated mileage or mileage you find on a car fax is too subjective to mean anything on a 30+ year old vehicle with more than one owner...
And it's Transfer Case & Axles have had something done to them several times if original...
Unless I missed it, one key thing to check on K5's is frame cracks and or repairs by all the shock mounts and their mounting tabs, brackets, etc...
Also, crossmember, frame cracks and or repairs opposite the steering box, near the fuel pump on a small block chevy...
Finding a K5 without frame cracks by the steering box and or shock mounts at frame and or mounting tabs is also edging into Unicorn Territory, how bad the unrepaired cracks are or repair job is on previous cracks is something to be mindful of...
I'll add a note on Salvage Titles, it's true stuff can be totaled by insurance companies for what may not seem signifigant to many...
The problem is it's forever a salvage title and the vehicle will have little or no resale value no matter what you do to it and you'll have dificulty getting insurance on it, and will pay more from those who will insure a branded salvage vehicle...
When it comes to buying a K5 now days you're buying a project or a restoration, with few exceptions...
IF you want a K5, unless it's had a frame off restoration by Gas Monkey Garage or Count's Kustom's or some other well known shop, you're going to have to do some work on it, probably a lot more often then not...
When it come's to pulling the trigger on a K5 for myself who like most can't afford to buy a restored one done right, I have some numbers in my head, like the cost of a crate engine, transmission, transfer case, rebuilding or replacing axles, rust repair, etc...
I'm in the running and driving project camp, if I find a K5 that run's and drives, has a clean title in the name of seller, in hand, and I don't think it needs one of everything right away and the price is what I'm willing to spend that day I might pull the trigger on it.