The typical asking rate per listing is in the $50's per square foot per year. The O'Fallon submarket is seeing a an increase in rates. In the last 3 months, the median rate rose $22 per sqft per year. That's a 61% increase in rent.
In the last 90 days, 9 listings have been listed, which means new availabilities most likley are leasing quickly. You'll want to be prepared to tour spaces as quick as possible. About 44% of the available space in the O'Fallon 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 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 1,400 sqft. Most properties in this area are approximately 1 stories. Most buildings in this area were built in 1999 and are Class B.