I agree with the previous post. It all depends on condition, originality, and how much work it will take to use the camper.
We bought ours for $1000, but it was very, very tired. The quick synopsis is that it needed to be gutted, rotten subfloor removed, rotten frame repaired, new subfloor put in, and then on to rebuilding the interior. We are more than 8 years into our project, and it is about 80% finished. We do a bit more each season and enjoy the trailer every time.
I have a bit more than $1000 in it now!! What could I sell if for? It's not for sale, but I am betting 10x what I paid. Little Airstreams are counter to modern culture...they go against the "bigger is better" concept and will always be worth more than their big cousins.
"The difference between vintage and retro is that vintage is honestly old and cool. Retro tries to be but isn't."