a lot of major cities require you to get a "busking liscense". i had never heard of this until i got into a little trouble in downtown kansas city. i bet you could make a lot playing in san francisco, id advise playing your sax vs guitar, you see a lot of guitarists busking, not as many sax players. sounds fun!
most we made is about $60 in two hours between several of us, but it is always a blast and youll likely meet some interesting people.