As a sidenote, I'm not sure I've ever met anyone who regards the ~650 km trek from SF to LA as "fun", unless somehow they're flying their own private aircraft there. Obviously, there are many options to travel between the two major population centers of California, including: commercial aircraft, private bus line, nationally-operated Amtrak, state-sponsored Amtrak California, private automobile, bicycle, and good ol walking.
Not to say all of these are equally popular, but compared to many places outside the USA, getting between these two hubs really ought to be cheap, yet it's not. The best chance at fixing that is by rail, which of those aforementioned choices, moves the most people at once, has the widest catchment area along the line, is only moderately expensive, and dove-tails into existing urban transit in SF and LA.
No, I'm not talking about California High Speed Rail, although I'm looking forward to that one too. That said, HSR serves a different role: geting to LA in the shortest possible time, since airport delays mean HSR's 350 kph can be faster than an airplane's 1100 kph + 0 kph waiting in the TSA line.
Rather, I'm talking about conventional rail corridors that already exist and just need a few upgrades to support additional passenger service. Adding passing tracks to freight corridors mean trains can move along at some 79 MPH (127 kph), which is both competitive with automobile speeds but trains carry so many more people than even two or three buses. The cost per passenger is thus potentially very low, getting us closer to that $20 figure while also being "easy" to ride. The state is already making this happen, although it'll take time for ridership to ramp up, which will allow the fares to drop.
Is a train considered "fun"? I personally think so, but others might value not being felt up by TSA or the ability to have a drink while admiring the coast through the window.