There is a reciprical arrangement with the Franklin Institute of Philadlephia, too, so that if you have a membership to one, you can visit the other for free. I'm looking forward to checking this out on our trip in a couple of months!
I joined Science Museum of MN thru a special program at a discounted price (aimed at people with low income --can enroll if on state funded health programs ,WIC, Section 8 etc.).
$44.50 for family membership (DH is disabled and qualifies for a special type of medical aid), regular $89.
Some day I plan to make use of the passport program and go to the great museums in Chicago !