The typical asking rate per listing is in the $10's per square foot per year. The Alexandria submarket is going through a a rise in rates. In the last 3 months, the median rate increased $16 per sqft per year.
In the last 90 days, 19 listings have been listed, which means office spaces are probably 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 2,020 sqft. Most buildings in this area are close to 1 stories. Most buildings in this area were built in 0 and are Class B.