Welcome to the Forums!
Step 1 in the search for a vintage Airstream is to manage your expectations and to make sure you have a realistic budget for the project. You might get hold of the old episodes of the Vintage Airstream Podcast (The VAP). These episodes discuss a lot of aspects of what to expect from a Vintage trailer.
There are many threads on these forums that discuss how to evaluate if an axle is shot (try doing a google search from outside the forums for "airforums axle worn out" and you will get half a dozen threads to look at). If you are buying a 40 year old trailer that is still riding on the original axle, you can pretty much guarantee that the axle needs to be replaced, as they only have an expected lifespan of about 20-25 yrs.
If axles seem expensive, hold onto your hat! You won't find the curved panoramic (front corner) windows for an Argosy for less than $500 apiece, and things like original shower pans in good condition are very difficult to find (as they get old and disintegrate and they are no longer manufactured).
Yes, many of us dream of picking up a road-worthy trailer for a few thousand dollars that only needs some cosmetic sprucing up (I was there myself), but so many of these turn into shell-off rebuilds when the new owner discovers that the floors are rotten, the frames are rusting away, the walls are infested with mice, etc., etc..