In reply to simonwhittle: I went Nov 06 and explored that option, there is a greyhound bus from LA to Reno which stops in Bishop.
Once you're there it could prove tricky thumbing lifts to the climbing areas each day though if you're staying in town. There is a camp site close to the Happy/Sad boulders but it isn't the best.
Camping up at the Buttermilks would be a bit of a rough one, there are no showers etc at any of the campsites up there and the river water is COLD!
If you can stretch to the extra cash (local hire is much cheaper than booking over here) then I'd say definately get a car, even it's just hiring in Bishop to save on fuel on the way up there.
If you can't afford the car Bishop locals are some of the friendliest around, I'm sure they'll be nice to you. Hope this helps.