On average, listings lease in the $10's per square foot per year. The Affton submarket is going through a a rise in rates. In the last 3 months, the median rate rose $17 per sqft per year.
In the last 90 days, 2 listings have come on the market, which means new availabilities are probably going fast. You'll want to be prepared to make an offer immediately. 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 1,300 sqft. Most buildings in this region are approximately 2 floors. Most buildings in this region were built in 2001 and are Class B.