Right now, American Airlines (
http://www.aa.com ) has nonstop roundtrips between Chicago-O'Hare (ORD) and Orlando International (MCO) for as little as $112.90 nonstop for some departures this month. And American has lots of roundtrips through early December for under $200. I played around a bit on their website, and I repeatedly saw $176.90 or a few dollars more than that.
Ted (
http://www.flyted.com ), a part of United Airlines, offers similar roundtrip fares between ORD and MCO.
I book several roundtrips between ORD and MCO each year. If your flight involves a date that is likely to be very popular, such as the weekend when spring break or winter break begins for most Chicago schools, book as early as possible -- the fare will almost cetainly go up. For example, for our cruise in March 2004, I booked 331 days before our return day. The fare was $198 roundtrip. The fare kept going up and up, and was over $1,000 roundtrip a month or so before we flew. For "ordinary" days, watch for a good airfare. I consider $179.90 to be very good. Sure, the fare may go down if you wait, but it could go up and stay up.
Keep in mind that the day of the week and the time of the day can make a huge difference. It sometimes really pays to fly a day earlier and stay in an airport hotel the first night.
Finally for flights between Chicago and Orlando, I almost always avoid connections. By the time you factor in the ground time in the connecting city and the second flight, you're losing around 3 or even 4 hours. That's the difference between having a day that includes fun and travel and a day that's essentially only travel.