I think that maintenance really plays a good part in this,  unless you
charge the host for maintenance.  In our case,  since the exhibit contains
a large number of vintage electronic devices and systems, this wasnt
really possible or fair in our view.  We simply broke down the cost of
research, construction etc.  as well as a percentage of estimated
maintenance and a view towards putting a portion of the proceeds away
towards future preservation.

I feel that was a fair method of arriving at a price,  especially with the
benefits that host museums gain from hosting high-profile and "publicly
attractive" exhibits.