I agree with John Simmons' opinion that Natural History Collections
should not be assigned a monetary value.  The specimens have an
intrinsic value; they are priceless.   Intrinsic means, that by
definition their value is: "...belonging to the real nature of a thing;
not dependent on external circumstances..."  External circumstances
such as market value change depending on demand.  Demand is influenced
by collectors, hobbyists and what may be "in vogue", rather than
the scientific value to a researcher or the educational value provided
to a student or member of the public.
 
Just my (strong) opinion...
Carol K. Malcolm
Texas Natural History Collection
Texas Memorial Museum-UT Austin