Most listings are in the $20's per square foot per year. The Ashburn region is going through a decrease in rates. In the last 3 months, the median rate fell $5 per sqft per year. That's a 15% decline in rent.
Compared to the rest of the Washington D.C. market, the Ashburn submarket has lower rates, so you should have no trouble finding a great deal in this discounted submarket.
In the last 90 days, 17 listings have come on the market, which means office spaces are probably going fast. You'll want to be prepared to make an offer immediately. About 12% of the available leases in the Ashburn 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 1,700 sqft. Most buildings in this region are approximately 2 stories. Most buildings in this area were built in 2000 and are Class A.