Verner Panton showed the Flying Chair at the 1964 Cologne Furniture Fair as part of a total Panton environment. It caused a sensation, but it was never put into production, and only a couple of installation photos survived.
In 1998 Vitra produced a handful of Flying Chairs under Panton's supervision for a traveling exhibition of Panton's work, that rode the wave of the designer's revival. [Another Vitra-curated show, in NYC in 2005, included Flying Chairs, too.] A few--or the same one, over and over--have turned up at auction, starting in 2002. One didn't sell in 2007 for EUR6,500-7,500, and the last sale price I can find is a May 2005 sale at Phillips for $5,760.
So that should give you some idea of where to start your haggling with Hamburg Modern, which has one for sale right now.
Verner Panton, Flying Chair, price on request [hamburgmodern.de]
