On average, listings lease in the $20's per square foot per year. The River Forest region is seeing a a boost in rates. In the last 3 months, the median rate increased $24 per sqft per year.
Compared to the rest of the Chicagoland market, the River Forest submarket has lower rates, so you should have no trouble finding a great deal in this discounted submarket.
In the last 90 days, 1 listings have been made available, which means new listings are probably leasing quickly. You'll want to be prepared to make an offer immediately. 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 1,500 sqft.