Most listings are in the $10's per square foot per year. The Irving Park region is seeing a a boost in rates. In the last 3 months, the median rate increased $16 per sqft per year.
Compared to the rest of the Chicagoland market, the Irving Park region has smaller rates, so you should have no trouble finding a great deal in this discounted submarket.
In the last 90 days, 1 listings have been listed, which means new availabilities most likley are leasing quickly. You'll want to be prepared to make an offer immediately. 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 800 sqft. Most properties in this market are around 2 stories. Most buildings in this area were built in 1952 and are Class B.