The typical asking rate per listing is in the $10's per square foot per year. The Westchester region is going through a an increase in rates. In the last 3 months, the median rate went up $19 per sqft per year.
Compared to the rest of the Chicagoland market, the Westchester submarket has lower rates, so you should have no trouble finding a great deal in this undervalued region.
In the last 90 days, 55 listings have been listed, so you'll want to check back regularly for new listings. About 15% of the office spaces in the Westchester are subleases, so you might be able to find a shorter term or below market rent. 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 2,390 sqft. Most buildings in this area are close to 2 floors. Most buildings in this region were built in 1986 and are Class A.