On average, listings lease in the $10's per square foot per year. The Greenbelt submarket is experiencing a decline in rates. In the last 3 months, the median rate fell $15 per sqft per year. That's a 48% decrease in rent.
Compared to the rest of the Washington D.C. market, the Greenbelt region has smaller rates, so you should have no trouble finding a great deal in this depreciated region.
In the last 90 days, 10 listings have come on the market, which means leases most likley are leasing quickly. You'll want to be prepared to make an offer immediately. About 40% of the available leases in the Greenbelt are subleases, so you might be able to find a shorter term or below market rent. There aren't many listings below 2,000 square feet available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 2,000 sqft. Most properties in this area are around 8 stories. Most buildings in this market were built in 1986 and are Class A.