The typical asking rate per listing is in the $30's per square foot per year. The Fairfax County region is seeing a decline in rates. In the last 3 months, the median rate decreased $1 per sqft per year. That's a 2% decline in rent.
In the last 90 days, 25 listings have come on the market, which means spaces 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 posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 2,340 sqft. Most properties in this market are close to 5 floors. Most buildings in this market were built in 1985 and are Class B.