On average, listings lease in the $20's per square foot per year. The Northbrook submarket is going through a decline in rates. In the last 3 months, the median rate decreased $3 per sqft per year. That's a 11% decrease in rent.
Compared to the rest of the Chicagoland market, the Northbrook region has less expensive rates, so you should have no trouble finding a great deal in this discounted region.
In the last 90 days, 30 listings have been listed, which means new listings are probably going fast. You'll want to be prepared to tour spaces as quick as possible. About 3% of the listings in the Northbrook are subleases, so you will probably have to consider a longer term lease. 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 1,760 sqft. Most properties in this market are close to 4 floors. Most buildings in this region were built in 1980 and are Class A.