Most listings are in the $10's per square foot per year. The Mission submarket is experiencing a decline in rates. In the last 3 months, the median rate fell $6 per sqft per year. That's a 27% decline in rent.
In the last 90 days, 28 listings have been made available, which means new availabilities most likley are going fast. You'll want to be prepared to make an offer immediately. 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 2,470 sqft. Most buildings in this region are around 2 stories. Most buildings in this area were built in 1972 and are Class B.