The typical asking rate per listing is in the $10's per square foot per year. The Glen Ellyn region is going through a a boost in rates. In the last 3 months, the median rate increased $18 per sqft per year.
Compared to the rest of the Chicagoland market, the Glen Ellyn submarket has smaller rates, so you should have no trouble finding a great deal in this undervalued submarket.
In the last 90 days, 5 listings have come on the market, which means listings are probably leasing quickly. You'll want to be prepared to make an offer immediately. About 20% of the listings in the Glen Ellyn are subleases, so you might be able to snag a great spot on a short term. There aren't many listings below 2,000 square feet on the market, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,000 sqft. Most buildings in this area are close to 1 floors. Most buildings in this area were built in 1983 and are Class A.