Most listings are in the $0's per square foot per year. The North Riverside submarket is seeing a decline in rates. In the last 3 months, the median rate fell $30 per sqft per year. That's a 100% decline in rent.
In the last 90 days, 0 listings have come on the market, which means leases most likley are going fast. You'll want to be prepared to make an offer immediately. About NaN% of the listings in the North Riverside are subleases, so you will probably need to consider the implications of signing a direct lease with the building. 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 sqft. Most buildings in this market were built in 1972 and are Class B.