Anywhere from 5k for a fixer or seller unaware of value, to 10k for one in fair shape needing some work, 20k for a nice solid example ready to go camping, to 35 to 45k for a fully polished and refurbished beauty. From what I have seen, I would not expect to pay under 20k for something you will be happy with, needs nothing, solid example, but you can also get lucky.
Maybe worth digging through the Airstream Archives (they have floor plans, specs, optional equipment lists) and for the our 1975 Argosy I found the specification list, with pricing.
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