Most listings are in the $30's per square foot per year. The Fairfax submarket is experiencing a decrease in rates. In the last 3 months, the median rate decreased $1 per sqft per year. That's a 2% decrease in rent.
Compared to the rest of the Washington D.C. market, the Fairfax region has smaller rates, so you should have no trouble finding a great deal in this discounted submarket.
In the last 90 days, 32 listings have been posted online, which means 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 2,300 sqft. Most properties in this area are close to 5 stories. Most buildings in this area were built in 1985 and are Class B.