Chicago Land has lots of stuff to do, that don't cost too much.

Reasons to agree: +6

1. If you are lucky you can find parallel parking for free around Lincoln Park Zoo.
2. Parking is $1.00 an hour, if you can find any, near Northerly Island. I drove there with 2 bikes in  my car, and my 7 year old son, and we rode to Millennium Park and back. 
3. Kids ride the Metra free on the weekends. 
4. The Water Tower Place Mall does parking validation. 
5. It costs $7 per adult to ride to Chicago Union Station (week-end passes, kids ride free). From there you can walk to a number of places:
1. Millennium Park. 
1. In the summer, kids can play in the fountain. Bring towels, and a change of clothes. It is sort of white trash, but they can change in the bathrooms. 
2. Each time you go down the kids will probably want to look at the bean, and get their photo taken.
3. I should probably walk the whole park once. Their are some statues on the south end I have never seen. 
2. Winter
1. Kris Kringle Market Chicago 
3. We walked, with 3 kids, and 2 strollers, all the way to the Hancock Building. It was a pretty long walk. When we got back to Navy Pear we took a water taxi bat to Union Station, to save our legs, and to make a train.
6. Apparently a portion of the Field Museum is free. Parking is not free, and I don't think a train will get you there. If you walk from Union Station, head straight for the lake, as some of the neighborhood between the two can be a little dicey. I guess you could ride a buss, but figuring out a train schedule is pushing it for me, as I don't make it into the city very often. Adding a bus schedule might be a little much. Also I don't like cabs, but you can figure your own life out, OK?

Reasons to disagree: -5

1. Sales tax is high in Chicago.
2. It costs $20 at a minimum to park in Chicago. 
3. It cost $7 for a weekend pass. So if you want to go in as a couple it costs $14 just to get there. 
4. The Stained Glass Museum, Navy Pier is boring. Who cares?
5. The Frank Gehry-designed Jay Pritzker Pavilion may be "the most sophisticated outdoor concert venue of its kind in the United States" but it is more likely the best example of overly ornate-as-a-substitution-for-sophisticated" outdoor museum in the USA. It is not worth going to, just to look at, unless their is a concert. 
6. Navy Peer is kind of stupid... They have a Ferris-Wheel, but so does the state fair... sure it gives you a great view, but so does walking along the beach. Then there is not much else to see. OK. OK. I've never actually paid to ride the Ferris-Wheel. I hear it is sort of cool. In fact, I wouldn't mind going on it... But I imagine if your drove a long way to See Chicago, and all you did was go to Navy Peer, which I imagine some people do... then you would probably be disappointing .. I only critisize it because I am amazed at how many millions of people visit it each year... I don't hat crowds as much as my wife, and so I wouldn't mind going back.

Score:

# of reasons to agree: +6

# of reasons to disagree: --6

# of reasons to agree with reasons to agree: +7/2 = 3.5

# of reasons to agree with reasons to disagree: -0

Total Idea Score: +4.5

Webpages that agree:

1. http://www.groupon.com/local/chicago/things-to-do
2. http://www.wolfstad.com/2006/01/top-10-budget-things-to-do-in-chicago/
3. http://thelocaltourist.com/cities/chicago/cheap-things-do-chicago
4. http://gochicago.about.com/od/attractionsandlandmarks/tp/free_chicago.htm

Images that agree:

My son at Millennium Park on our Chicago Bike Ride

You don't have to pay anything to look at this brachiosaurus outside the Chicago Field Museum.