Use a checklist to conduct a serious inventory of of what you must repair or replace to make it roadworthy. Don't let the shiny aluminum blind you to the truth.
Remember, while not insignificant, the purchase price will be less than what you will spend to make it something you can use.
That said, a 1977 Sovereign
in unrestored, original condition is worth $3,800 to $5,800. Plan on replacing the following for starters:
Air conditioner, refrigerator, converter, batteries, tires, wheel bearings...
It is likely the axles will need replaced as well.
If you can do the labor yourself and have a place to work on your Airstream, you can control costs, otherwise it's an expensive proposition.
Remember, Tom's RV in Albuquerque charges $95.00 per hour.
Use a checklist to determine what you may be getting yourself into.
This is a 1976 Sovereign
I restored (partially):