I have nothing planned yet (the key word here is planned), but from the Bay Area it's easy enough (though a bit longer time-wise) to get to Yosemite Valley via Amtrak. Amtrak uses a combination of buses and trains (the San Joaquin) to transport people to and from the Bay Area and Yosemite. Last time I checked, the prices were pretty reasonable.
And if you're planning to travel to Yosemite during a weekend, most car rental companies like Hertz and Budget offer very low car rental rates for weekend rentals (rent the car on Thursday afternoon or later and return the car by Monday morning). Those rates are typically $25 per day or even less (I've rented as low as $14 per day) for a weekend rental of an economy car (like a Ford Focus) from a local (non-airport) car rental location and the rentals typically include unlimited mileage.