i paid 900 bucks for my first airhead, a 78 r100s. it ran, but needed 400 dollars in brake hydraulics, and 650 dollars in back reg. fees, so by the time i got it operable and fresh rubber on it, i was in it about 2500. sold for 3k
then i got a GS last Dec, salvage title for 3700, and it promptly needed 2400 in major repairs. parted it out after the 3rd mega repair was needed
picked up an r80 mono for 3600 in good shape with 75k on it,
they're worth whatever someone will pay.