The typical asking rate per listing is in the $20's per square foot per year. The Ashburn region is going through a decline in rates. In the last 3 months, the median rate fell $3 per sqft per year. That's a 9% decrease in rent.
Compared to the rest of the Washington D.C. market, the Ashburn submarket has less expensive rates, so you should have no trouble finding a great deal in this depreciated region.
In the last 90 days, 23 listings have been posted online, which means new availabilities most likley are leasing quickly. You'll want to be prepared to make an offer immediately. 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 2,370 sqft. Most properties in this area are around 2 floors. Most buildings in this area were built in 2001 and are Class A.