Don't know about the Big Sur area, but for the Monterey area;
Parking is easier to find in Sand city [the town just North of Monterey],
Look in the neighborhood North side of HWY 218, between Del Monte Blvd and Fremont, I spent some nights on Elm just west of Fremont, good place for that, Lots of stores and places to eat right there, no one bothers you, safe area.
You can beach park for free all day near there; Canyon Del Rey Blvd right on the other side of HWY 1, there's porta-potties, trash cans, and a Home Depot right there.
Another place to spend the night is Lighthouse Ave [Monterey] just near Ocean View Blvd, then during day spend it on a very beautiful Asilomar State Beach, free all day parking right near the water, [get there early], its one of the best free beach parking places I have seen in Calif.