Visiting and want to go to Muir Woods - How?

I surprised my girlfriend with a trip to SF for her birthday and I've heard Muir Woods is a must see. I'm wondering what the cheapest way to get there would be. We're staying at a hotel near Fisherman's Wharf and don't have a car. The concierge told me that the only way to get there was a tour which is a combined with Sausalito for $49. There's got to be another way, right? Are there any buses that drop off there? Any other options? Thanks reddit.