I have built successfully a Van de Graaf generator for improving lab
equipement, this generator is able to produce up to 250kV in dry air, the
material used is common and cheap ( about 50 US$ (300 French Francs) without
the DC motor ).
This is a wonderfull tool for exploring electrodynamics and electrogravitics
domains.
You will find all pictures and diagram for building this Van de Graaf
generator at :
http://ourworld.compuserve.com/homepages/jlnaudin/html/jlnvdg.htm
I hope that this will interest you.
Sincerely,
Jean-Louis Naudin (France)