On average, listings lease in the $30's per square foot per year. The Greenbelt region is going through a a rise in rates. In the last 3 months, the median rate rose $1 per sqft per year. That's a 2% increase in rent.
Compared to the rest of the Washington D.C. market, the Greenbelt region has greater rates, and you'll need to pay a premium to be in this hot region.
In the last 90 days, 10 listings have been listed, which means leases are probably leasing quickly. You'll want to be prepared to make an offer immediately. About 90% of the available space 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 posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,280 sqft. Most properties in this area are around 8 floors. Most buildings in this region were built in 1986 and are Class A.