In the last 90 days, 1 listings have been posted online, which means leases most likley are going fast. You'll want to be prepared to tour spaces as quick as possible. About 600% of the listings in the Mission are subleases, so you might be able to sign a shorter term by taking over a previous lease. 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 sqft. Most properties in this area are close to 1 floors. Most buildings in this market were built in 2006 and are Class A.