On average, listings lease in the $20's per square foot per year. The Falls Church County region is going through a decrease in rates. In the last 3 months, the median rate fell $2 per sqft per year. That's a 8% decline in rent.
In the last 90 days, 1 listings have been posted online, which means office spaces most likley are going fast. You'll want to be prepared to tour spaces as quick as possible. About 600% of the listings in the Falls Church 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 available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 2,040 sqft. Most properties in this region are around 2 floors. Most buildings in this area were built in 1980 and are Class B.