Airline pricing has been greatly impacted by the recession, but nothing seems to impact it more than some good old fashioned competition.  The Chicago to Minneapolis route is featured in the article linked below.

I can tell you from personal experience that flights on this route even with 21-day advance purchase were in the neighborhood of $400+ late last year but once Southwest Airlines announced that they were expanding with several flights a day on this route the price fell to under $100.  Recently they are as low as $88 on many airlines (American, United, Northwest, & Southwest all fly this route) and flights to nearby Milwaukee are also under $100 as AirTran has expanded into that market to compete with a faltering/retrenching Midwest Airlines. Unfortunately, flying from MSP to MKE on AirTran currently requires a layover in Atlanta but that is changing soon.  Interestingly enough, the prices on the MSP to Chicago route were cheap before AirTran abandoned that route last year.

Read the article at this link: http://www.marketwatch.com/news/story/story.aspx?guid={BCA6AD1A-6A63-4D94-8351-52B8F5A8EAE3}&siteid=rss