Most listings are in the $20's per square foot per year. The St. Louis County submarket is going through a a boost in rates. In the last 3 months, the median rate went up $2 per sqft per year. That's a 7% rise in rent.
In the last 90 days, 411 listings have been made available, so you'll want to check back regularly for new listings. About 4% of the available space in the St. Louis County are subleases, so you will probably have to consider a longer term lease. There aren't many listings below 2,000 square feet available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 2,400 sqft. Most buildings in this area are close to 2 floors. Most buildings in this area were built in 1982 and are Class B.