Ive lived in the Mission since 2001...within a few blocks from 16th & Mission. I try to avoid it at night as much as possible. There is a lot of illegal activities that go there and while I dont feel scared that someone will do something to me, its just a lot of crazy action and you never know what is going to happen. Its not tooo bad while BART is open, or on nights there is an event at The Chase Center, there is extra security around the BART because of the shuttles that go between the 2 plqces. After BART closes it is much more scetchy.

Aside from airbnb, Have you tried looking on craigslist for people renting rooms? For your price range you could find a nice place, and meet some people, maybe.....