In the attic looking for something else I came across this "Used Instrument List, no. 5" from Elderly, dated Jul 21, 1982. There are about 30 mando family instruments listed; here's a few:
Martin A 1941 $265
Gibson F-4, c.1920 $1,400
Gibson A-1 c.1914 $400
Gibson A-1 c.1917 $475
Gibson A-3 c.1915 $550
another half dozen Gibsons in the $300-500 range and another F-4 for $1300.
I'm not drawing any conclusions from this but it's interesting to compare today with 23 years ago.