This was by far the least expensive tour bus company that we found, (and I think we checked everyone in the bay area.)

They picked up our 35 of our guests in downtown San Francisco, and transported across the Golden Gate Bride to Marin, and brought them back at the end of the night. Although I did not personally ride the bus, my guests said it was very smooth. Also, it was a nice for out of town guests who didn't have to rent a car or navigate roads in an unfamiliar area.

I highly recommend.