I think your best options are Mado, Lula, and Frontera Grill.  All three are reasonably-priced, open for lunch, work very closely with local farmers (and in the case of Frontera, grow their own), and have very good food.

http://www.madorestaurantchicago.com/

http://www.rickbayless.com/res…..grill.html

http://www.lulacafe.com/

Best,

Michael

I'd add the Bristol - rapidly becoming one of my favorite places in Chicago.  Few restaurants are more committed to local farmers.  Burger with duck fat fries, and a huge fried egg and pork belly sandwich are each 10 bucks.