I was pretty sure that I'd seen somewhere that the price of typical
general aviation airplanes were, relative to median annual income, about
the same ratio as they had always been. I'm still not sure whether that
is true, but according to GAMA, another number, the historical price of
4 seat entry level airplanes (among others) has risen faster than the
cost of inflation, houses, or autos.

Pages 11 to 19 of this GAMA document are of particular note:

http://www.faa.gov/news/conferences_...rcraftGAMA.pdf

The document appears to be PDF coversion of a PowerPoint presentation,
so is missing explanations and references.