You ask an impossible question as the value greatly depends on the condition of the trailer. I would speculate 72 Sovereign
values can range from $5000 for a basket case to $70,000 for a beautifully and completely renovated one.
The aluminum body is the most expensive part of a vintage Airstream. Many 70s trailers have rusty frames and subfloor rot causing rear end separation. This is an expensive repair. Then there are the axles which would cost maybe $3000 to replace with new.
Start studying the Classified in these Forums for comparables and their asking prices. If you really want to know, have this trailer appraised.
WBCCI #8607 VAC Region 11
KnowledgeBase trailer renovation threads: 69 Globetrotter, 76 Sovereign, 75 Overlander, 66 Trade Wind Such fun !