On average, listings lease in the $30's per square foot per year. The South Loop region is going through a an increase in rates. In the last 3 months, the median rate rose $3 per sqft per year. That's a 9% increase in rent.
Compared to the rest of the Chicagoland market, the South Loop region has more expensive rates, and you'll have to negotiate above asking rent to be in this hot submarket.
In the last 90 days, 20 listings have come on the market, which means leases might be leasing quickly. You'll want to be prepared to tour spaces as quick as possible. About 5% of the listings in the South Loop are subleases, so you will probably need to consider the implications of signing a direct lease with the building. There aren't many listings below 2,000 square feet on the market, so finding a space for a small business might be tough.
Even though the median size is 4,650 sqft, there are still 0 office spaces below 2,000 sqft. Most properties in this market are close to 3 stories. Most buildings in this market were built in 1920 and are Class B.