Compared to the rest of the Chicagoland market, the South Loop submarket has greater rates, and you'll have to negotiate above asking rent to be in this hot submarket.
In the last 90 days, 22 listings have been listed, which means new listings most likley are going fast. You'll want to be prepared to make an offer immediately. There aren't many listings below 2,000 square feet available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 2,090 sqft. Most properties in this area are around 3 stories. Most buildings in this market were built in 1920 and are Class B.