Most listings are in the $30's per square foot per year. The Fairfax region is experiencing a a rise in rates. In the last 3 months, the median rate went up $31 per sqft per year.
Compared to the rest of the Washington D.C. market, the Fairfax region has less expensive rates, so you should have no trouble finding a great deal in this discounted region.
In the last 90 days, 31 listings have come on the market, which means leases might be leasing quickly. You'll want to be prepared to make an offer immediately. About 190% of the available space in the Fairfax are subleases, so you might be able to snag a great spot on a short term. 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 1,210 sqft. Most properties in this area are approximately 3 stories. Most buildings in this area were built in 1985 and are Class B.