On average, listings lease in the $30's per square foot per year. The Fairfax County region is experiencing a decline in rates. In the last 3 months, the median rate decreased $1 per sqft per year. That's a 2% decrease in rent.
In the last 90 days, 31 listings have been listed, which means new 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 available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,180 sqft. Most buildings in this market are around 5 stories. Most buildings in this area were built in 1985 and are Class B.