Most listings are in the $10's per square foot per year. The Dahlgren submarket is seeing a a boost in rates. In the last 3 months, the median rate increased $16 per sqft per year.
In the last 90 days, 8 listings have been posted online, which means listings most likley are going fast. You'll want to be prepared to make an offer immediately. About 13% of the available space in the Dahlgren are subleases, so you might be able to sign a shorter term by taking over a previous lease. 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 1,000 sqft. Most properties in this area are close to 2 floors. Most buildings in this market were built in 1991 and are Class B.