How much will renovation cost? That depends on you and the condition of the airstream you buy. Renovating an airstream is like renovating a home. The better the condition of the airstream the less work that will need to be initially done. Your personal tastes and the amount you will want to individualize your airstream are also factors that will effect the total price.
My suggestion to you is buy an airstream that is in good mechanical condition but needs cosmetic updating. If you buy one that needs a frame off restoration it will be like buying a house that needs to be stripped down to the studs and totally rebuilt.
Good luck and have fun. I bought my
1963 Globetrotter in 2000. Every year I make one major improvement to my GT. By taking it slow and easy, I have not broken the bank and more importantly I have not gotten sick of the project.