Most listings are in the $10's per square foot per year. The Mission region is seeing a decrease in rates. In the last 3 months, the median rate fell $2 per sqft per year. That's a 9% decrease in rent.
In the last 90 days, 30 listings have been posted online, which means office spaces are probably going fast. You'll want to be prepared to make an offer immediately. About 3% of the office spaces in the Mission are subleases, so you will probably need to consider the implications of signing a direct lease with the building. 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 2,080 sqft. Most properties in this area are approximately 2 floors. Most buildings in this market were built in 1972 and are Class B.