The typical asking rate per listing is in the $10's per square foot per year. The Mission region is going through a an increase in rates. In the last 3 months, the median rate rose $17 per sqft per year.
In the last 90 days, 30 listings have come on the market, which means leases are probably going fast. You'll want to be prepared to make an offer immediately. About 30% of the listings in the Mission 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 available, 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 market are close to 2 stories. Most buildings in this market were built in 1972 and are Class B.