Is there a place one can get the historical price of new
planes for the past 10-20 years ? Want to know how the
price of planes moved up over the years.

Second question is about the price difference between the
manufactures and the dealers. Can one project that the bigger
the difference, the bigger potential for lack of product support
from the plane maker ?
There can be 25-30% difference between the price listed on the
manufacture's web site and those listed by the dealers.
E.g. Diamond DA40 is listed at about 240K on Diamond's web site,
but over 300K on the dealers. Pipers are similar. With Cessna's
being the exception, where the dealer price is about 6% above
the manufacture's.

P S