Although general not done for special expensive exhibits, most
museums with substantial admission fees offer free days or free
nights. I am sure that this was implemented in part due to the very
concerns you express. When I worked at small museums we
would discretionarily waive fees and had a special family rate. Desk clerks
do not always have the authority to do this. BTW Your paid admission
ticket buys you convenience and fewer patrons.
Don't think I'm unsympathetic. I'm a well-known cheap skate,
still in shock from the idea that it costs $40 to get someone to mow my lawn
today.