On average, listings lease in the $20's per square foot per year. The Fairfax County region is experiencing a a rise in rates. In the last 3 months, the median rate went up $30 per sqft per year.
In the last 90 days, 31 listings have been posted online, which means leases might be going fast. You'll want to be prepared to make an offer immediately. About 139% of the available leases in the Fairfax County 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 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 1,100 sqft. Most buildings in this area are approximately 3 stories. Most buildings in this market were built in 1985 and are Class B.