I am trying for the same nights. As of today, I have bid up to $130 for a 4* and up to $100 for a 3* in the North Michigan Ave and Millennium Park zones. It appears that it is possible to get a 4* for $85 on Hotwire for Thursday night only and a 4* for $120 on Priceline for Friday and Saturday, but I do not want to have to change hotels.