For hotels I would check out
www.hotwire.com. I used that and ended up with the Hard Rock which was in a really good location. Chicago has so many hotels that the hotwire map is split into fairly small areas, so you know where you'll end up.
I would definitely not stay at O'Hare. Almost two hours of every day are gone just taking the train there and back. Plus you can't go back to your hotel to get different clothes if the weather changes, or drop off the stuff you bought or change into something nicer for dinner etc. Just not worth it when you are paying that much to be somewhere.