Most listings are in the $20's per square foot per year. The Falls Church County region is going through a decline in rates. In the last 3 months, the median rate decreased $2 per sqft per year. That's a 8% decrease in rent.
In the last 90 days, 1 listings have been posted online, which means spaces most likley are leasing quickly. You'll want to be prepared to tour spaces as quick as possible. About 1,000% of the available leases in the Falls Church County 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 posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,050 sqft. Most properties in this region are close to 2 stories. Most buildings in this region were built in 1980 and are Class B.