You might see if there are any companies in your area that supply
display cases for 1) retail stores 2) expos/trade fairs.  I remember
looking into this once.  I think that you can probably find relatively secure
flat cases and shelving units.  You might also see if any of the libraries in
your area could lend this kind of thing, esp. university libraries.
Sometimes all they need is a new coat of paint.

Good Luck.

Riva Feshbach
Curator
DePaul University Art Gallery