The typical asking rate per listing is in the $10's per square foot per year. The Northbrook region is going through a an increase in rates. In the last 3 months, the median rate went up $19 per sqft per year.
In the last 90 days, 4 listings have been made available, which means listings might be 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 560 sqft. Most properties in this market are around 4 floors. Most buildings in this area were built in 1977.