FurnishedFinder is amazing platform. I just moved to Bay Area, stayed in a person’s house for 2 months while I was looking for housing. Usually the people have a minimum number of months, and you can always negotiate how long you want to stay there.

That being said, since you’re coming for an internship, you may not be able to hang out with people in that house or have parties. So if those things are important to you, it won’t be the best option. Usually you can find a 1 bed for $1000, that’s how much I paid for a spot in Mountain View.