Chicago is perfect for bidding hotels on Priceline as it has many areas you can do "free bid".
Be prepared to pay $30+ a day for parking if you stay in downtown area.
We have visited Chicago a few times as we like it very much in Summer time. The first time we had a car (no choice). We ditched our car at Rosemont Convention Center for 5 days and just took Blue Line to town every day. Subsequent visits we flew to Chicago and only took a rental car when we left Chicago going to Toronto and back.