On average, listings lease in the $30's per square foot per year. The St. Charles region is going through a an increase in rates. In the last 3 months, the median rate increased $37 per sqft per year.
In the last 90 days, 24 listings have been made available, which means listings most likley are going fast. You'll want to be prepared to make an offer immediately. About 17% of the listings in the St. Charles 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 available, so finding a space for a small business might be tough.
Even though the median size is 4,850 sqft, there are still 0 new listings below 2,000 sqft. Most buildings in this market are close to 1 stories. Most buildings in this area were built in 1993 and are Class B.