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 region.
In the last 90 days, 5 listings have been made available, which means spaces most likley are 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 sign a shorter term by taking over a previous lease. 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 1,000 sqft. Most properties in this region are approximately 1 floors. Most buildings in this market were built in 1983 and are Class A.