Small Office Space

The question speaks volumes ...
I know people small office space for as little as 200 a month, where will you find them?

Yes, I agree, craigslist would be your best bet.

SF currently has a vacancy rate of 9% offices, the average rental is about $ 30/square foot.

Here is the link for craigslist SF:
http://sfbay.craigslist.org/

An estate agent.

Craigslist.org. Here we are. But it depends on where you want your office space. IE: The "Square or the mission? Nob Hill or Fidi?

craigslist.org

Here is office space for rent, you can search by the maximum amount you wish to pay for the site.
http://sfbay.craigslist.org/off/