Most listings are in the $20's per square foot per year. The Manassas submarket is going through a decrease in rates. In the last 3 months, the median rate fell $3 per sqft per year. That's a 12% decrease in rent.
Compared to the rest of the Washington D.C. market, the Manassas submarket has less expensive rates, so you should have no trouble finding a great deal in this depreciated submarket.
In the last 90 days, 35 listings have come on the market, which means spaces most likley are leasing quickly. You'll want to be prepared to tour spaces as quick as possible. About 6% of the available leases in the Manassas are subleases, so you will probably have to focus your search on direct office leases. 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 2,190 sqft. Most properties in this area are close to 2 stories. Most buildings in this market were built in 1989 and are Class B.