Here's a great free idea for a mathematics exhibit, it deal's with the
realization and concrete description of infinity, a mathematical
phenomenon rarely explained in concise, visual, and appreciable terms.  We
start with a small museum given money from the feds, then we go out and
get a director (with a Ph.D. in?), who, because he loves his work so much,
does it for nothing, therefore he does not have to pay taxes.  Everybody
is happy right?
     He in turn solicits free ideas for this "museum" and gets the
physical exhibits built for free, because no money changes hands, its all
not-for-profit and tax deductible.  This museum has a free admission
policy so no one has to pay.  Great!  The museum has 250,000 visitors the
first year due to its proximity to no other free events for school
children, their parents and others.
      Soon however it is realized that the rest rooms, lighting, and air
conditioning is inadequate.  The call goes out for more grants and
donations to feed this truly unexpected  phenomenon.
     The director, too busy scheduling tours and volunteers (who grow
tired of the hordes descending on this great escape) has no time for grant
writing, decides it's time to go for well paid professional outside help.
Calling all his former socialist museum director friends in Russia he
realizes it doesn't exist anymore.
     Alas! I forgot about the plumbers and electricians.  Oh well so much
for infinity.  At least it was an attempt to define infinity and this
concept was also free of fees.

PS: Visuals upon request- A slight fee is required prior to shipment