I ran Chicago in 2004. I've forgotten the name of the hotel I used but it was out of town but on the "Orange Line" for the metro (or whatever the train is called). The orange line goes near the start/finish.
Try these two websites for cheaper fares. www.hotels.com and www.triprewards.com I use them all the time. (I'm a 50 States Marathoner - I ran 19 marathons in '05).
If you really want to be daring try www.hotwire.com for a really inexpensive fare - but you don't know the name of the hotel until you pay.
I used Hotwire.com once for the Flying Pig in Cincinnati. All the hotels were booked up. I ended up with a $39 hotel close to the host hotel!