On average, listings lease in the $20's per square foot per year. The Des Peres submarket is experiencing a decline in rates. In the last 3 months, the median rate fell $2 per sqft per year. That's a 7% decline in rent.
In the last 90 days, 8 listings have been listed, which means office spaces are probably going fast. You'll want to be prepared to tour spaces as quick as possible. About 25% of the available space in the Des Peres are subleases, so you might be able to sign a shorter term by taking over a previous lease. 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 1,310 sqft. Most buildings in this region are around 2 stories. Most buildings in this area were built in 1987 and are Class A.