You can do Chicago cheap for sure, especially if you use public trans, which can be a pain in the butt but it's cheap. I would priceline your hotel, you can get good deals that way, check River North, the Loop, North Michigan Ave.
HOWEVER, there is a lot of walking in Chicago if you aren't taking cabs. Even with public trans, I'm not sure if you could always work it out where you could take a bus to an L and never walk more than 2 blocks.
I take public trans everyday and so does my husband and we walk several miles each time if we are going to different places.
If you are going during the week you can save a ton at restuarants. I would look on yelp before you go because a lot of restaurants will run specials during the week, good prix fixe menus (did I spell that right lol), half priced wine and so on.
If you guys are foodies, I have a TON of recommendations
Kuma's (best burgers ever named after metal bands but this is a bar if you aren't into that kind of thing)
a good Chicago steakhouse like Gibson's or the Chop House, these are can be very expensive though
Bonsoiree
Piece (right of the L so very easy to get too, pizza and brewery)
There are a ton of good ones downtown if you don't want to travel far (Atwood, Bin 36, and so on).
Don't forget just walking around in Chicago is fun, you have Millenium Park, Lincoln Park Zoo, the lake.
Someone mentioned the Signature Room, I recommend the Signature Lounge instead on top of the Signature Room. And use the restroom, the ladies restroom has the same amazing view as the lounge!
