Most listings are in the $20's per square foot per year. The River Forest region is going through a a boost in rates. In the last 3 months, the median rate rose $24 per sqft per year.
Compared to the rest of the Chicagoland market, the River Forest region has greater rates, and you'll need to make a great offer to be in this hot region.
In the last 90 days, 1 listings have come on the market, which means spaces most likley are leasing quickly. You'll want to be prepared to tour spaces as quick as possible. 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 1,500 sqft.