We can teens get married for cheap in California

In another thread you said your boyfriend was 19, but how old are you? If you are under 18 you need parental permission.

As to where you can go, your local county courthouse or city hall can perform the ceremony. Generally for just the license fee. Which will vary by area.

http://www.sbcounty.gov/arc/marriage_info.htm

But if your boyfriend is homeless, marrying him is not a smart idea.. You shouldn't marry until you are financially stable.

At your home, in a nice city park, at the place where you meet, at the place where he asked you to marry him.

Many pastors do onsite weddings, craigslist should have dozens that do low cost weddings.

You can also get married at the court house, by the judge.