Most listings are in the $10's per square foot per year. The Fairfax region is going through a an increase in rates. In the last 3 months, the median rate rose $18 per sqft per year.
In the last 90 days, 6 listings have been made available, which means new availabilities most likley are leasing quickly. You'll want to be prepared to make an offer immediately. There aren't many listings below 2,000 square feet available, so finding a space for a small business might be tough.
Even though the median size is 3,360 sqft, there are still 0 new listings below 2,000 sqft. Most properties in this area are around 1 stories. Most buildings in this market were built in 2008 and are Class B.