On average, listings lease in the $40's per square foot per year. The Alexandria region is going through a an increase in rates. In the last 3 months, the median rate increased $9 per sqft per year. That's a 27% rise in rent.
Compared to the rest of the Washington D.C. market, the Alexandria region has higher rates, and you'll have to negotiate above asking rent to be in this hot region.
In the last 90 days, 150 listings have come on the market, so you'll want to check back regularly for new listings. About 1% of the available leases in the Alexandria 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 available, so finding a space for a small business might be tough.
Even though the median size is 3,200 sqft, there are still 0 office spaces below 2,000 sqft. Most properties in this area are around 5 stories. Most buildings in this area were built in 1984 and are Class B.