Most listings are in the $10's per square foot per year. The Mission submarket is seeing a decline in rates. In the last 3 months, the median rate decreased $2 per sqft per year. That's a 9% decline in rent.
In the last 90 days, 30 listings have been listed, which means listings most likley are going fast. You'll want to be prepared to make an offer immediately. About 3% of the listings in the Mission are subleases, so you will probably have to consider a longer term lease. There aren't many listings below 2,000 square feet on the market, 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 region are around 2 stories. Most buildings in this area were built in 1972 and are Class B.