Most listings are in the $20's per square foot per year. The Warrenton region is experiencing a an increase in rates. In the last 3 months, the median rate went up $21 per sqft per year.
Compared to the rest of the Washington D.C. market, the Warrenton submarket has less expensive rates, so you should have no trouble finding a great deal in this discounted submarket.
In the last 90 days, 3 listings have come on the market, which means new listings most likley are going fast. You'll want to be prepared to make an offer immediately. About 33% of the available leases in the Warrenton 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 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 1,470 sqft. Most buildings in this region are around 3 stories. Most buildings in this area were built in 1987 and are Class A.