There are many choices to tour San Francisco.
When you reach the Wharf area or visit the SF Convention and Visitor's Bureau, you cna pay for a tour to places like a ferry ride to Alcatraz, a ferry around some of the islands, a bus ride touring around all parts of town, renting a car or a motorcycle, and even a Segway!
The cheapest option is to get a free city map from the visitor's bureau and take the public transit. Be sure to take the Cable Cars, the country's only moving historical monument, and visit lots of the ethnic neighborhoods such as Chinatown, and Japantown.
Publc transit fares: $1.50 adult busses/metro
$5.00 one way Cable Car (regardless of age)
Note: The SF Visitor's Bureau website has a space where you can fill in your address and get free maps, guides, coupons for free stuff, and goodies.