In the last 90 days, 1 listings have been posted online, which means leases most likley are leasing quickly. You'll want to be prepared to make an offer immediately. About 300% 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 sqft. Most properties in this market are around 1 stories. Most buildings in this region were built in 2006 and are Class A.