Most listings are in the $10's per square foot per year. The Carol Stream region is seeing a decrease in rates. In the last 3 months, the median rate decreased $1 per sqft per year. That's a 4% decrease in rent.
Compared to the rest of the Chicagoland market, the Carol Stream submarket has lower rates, so you should have no trouble finding a great deal in this depreciated submarket.
In the last 90 days, 8 listings have been made available, 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 on the market, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 790 sqft. Most properties in this area are approximately 2 stories. Most buildings in this region were built in 1987 and are Class B.