Most listings are in the $20's per square foot per year. The Des Peres submarket is going through a decrease in rates. In the last 3 months, the median rate decreased $2 per sqft per year. That's a 7% decrease in rent.
In the last 90 days, 4 listings have been made available, which means new listings most likley are going fast. You'll want to be prepared to make an offer immediately. 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 1,310 sqft. Most properties in this region are around 2 floors. Most buildings in this region were built in 1987 and are Class A.