Most listings are in the $10's per square foot per year. The Florissant region is going through a an increase in rates. In the last 3 months, the median rate went up $1 per sqft per year. That's a 7% increase in rent.
In the last 90 days, 20 listings have been made available, which means office spaces most likley are leasing quickly. You'll want to be prepared to tour spaces as quick as possible. 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 320 sqft. Most properties in this market are close to 1 floors. Most buildings in this region were built in 1975 and are Class C.