oh I don't think that is the area you thinking of, 31st lot is just SOUTH of the McCormick Center, its like $40-$50 to park there, then you can either take the shuttle or walk about 15 mins or so.... got to go thru the long McCormick Place tunnel to then get to the Waldran Deck Lot, cross street, under Lake Shore Dr, then enter towards the stadium.....
The longest, saddest walk I had was thanks to Chris Conte....... @Irishman will remember it well. sigh......