You are probably likely to find more in the mission, and costs vary. I used to live in the Mission and I needed temporary parking for a few months while doing construction work and found one on Craigslist within a couple of days.
There are also larger parking garages that lease space by the month. As far as cost goes, generally speaking private parking will be in the $200's per month and a garage will be over $300.
I also found this parking search engine - http://sanfrancisco.bestparking.com/index.php#1 - that seems to have a lot but I cannot vouch for its accuracy.
Lance King/Owner-Managing Broker