Most listings are in the $20's per square foot per year. The Kirkwood submarket is going through a a boost in rates. In the last 3 months, the median rate rose $25 per sqft per year.
In the last 90 days, 12 listings have been made available, which means listings most likley are leasing quickly. You'll want to be prepared to make an offer immediately. About 25% of the available space in the Kirkwood are subleases, so you might be able to find a shorter term or below market rent. 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 1,460 sqft. Most properties in this area are close to 3 floors. Most buildings in this market were built in 2004 and are Class A.