Hello Tom -- and welcome to the Forums. Take a look at Vintage Airstream's Price vs. Condition
. These Forums over time will cover a lot of what a person needs to know in inspecting and determining what a fair price for a given Airstream might be. There is no crash course, so I hope you've been browsing for a while if you're considering this deal. A 30 year old trailer will have quite a number of needs unless it has been maintained in very usable condition -- and probably stored indoors.
How to restore? It's a long and complex process. You'll need to ask more about details as you go step by step -- but you've found the place to do that.
We lived in Silver Creek Township until 1988 -- but are not natives of the area.