Compared to the rest of the Chicagoland market, the Riverside submarket has higher rates, and you'll have to negotiate above asking rent to be in this hot submarket.
In the last 90 days, 1 listings have been listed, which means spaces are probably leasing quickly. You'll want to be prepared to make an offer immediately. About 100% of the available leases in the Riverside are subleases, so you might be able to find a shorter term or below market rent. There aren't many listings below 2,000 square feet posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,550 sqft. Most buildings in this area were built in 1871 and are Class B.