Hair extensions around San Francisco (CA)

I've been thinking and doing some research about hair extensions and the more I learn the more I get confused.
I have very fine thin hair (shoulder-length) and I'm looking for volume rather than length ( I don't want it to be obvious to my friends that i got extensions, I intend to keep it a secret)

I'm also on a tight budget, right now I'm willing to spend about $400 on something that would last about a year (is that even possible??)
I was considering clip-on hair extensions, are those any good??

I've read a post from a man who does hair extensions (weaving i guess) for $300 and then he charges $70 an hour every 3 months. If that's all the money it takes I'd be willing to do it.

Is there anyone around San Francisco who does hair extensions for these kind of prices? Please help me! I'm desparate to get hair extensions, I just don't know where and for how much.

Thank you,

Anna.