Biking from South Lake trail head to North Lake

[Hobbes]

I'm a fan of hitching. If you're at a major trail head, like S or N lake, there is always traffic coming/going, whether backpackers, fishers, day hikers, etc. The trick is to:
(a) hitch at the beginning of the trip, when you're all clean & fresh. (Just make sure you don't look like some scary character.)
(b) ask for rides amongst parked vehicles. Putting a thumb out against moving traffic is much harder.

In your situation, I would simply drive to S Lake, hang out around the area, watch & see who's doing what, then walk-up & approach someone about a ride. If you're friendly, it's pretty hard for someone to say 'no' when you're standing right there.

Even better, once you got near the junction of 168, offer them $40 or so to take you up to Sabrina or maybe even N lake. You'd be surprised how a little bit of cash motivates many people, especially since *they're almost already there*. No matter how you cut it, you'll never have to spend as much as a shuttle. They have significant insurance requirements, which is why their fees are relatively high.