We have been looking at the coast up there as a Plan B ourselves but are sticking with Plan A for now. With the heat we are experiencing inland the coast is going to fill up fast for the holiday. If you are considering going there instead, do it sooner rather than later or that won't be an option.
20 miles north of Fort Bragg is Westport Union campground. Right on the coast with ocean views but also right on the highway, so good and bad. Not very big and first come/first served so it typically fills up on weekends. Definitely will fill up for the holiday weekend. 20 miles south of Ft Bragg is a fairly unknown annex to Navarro River State Park right on the beach. Really nothing more than big parking spaces with picnic tables but hard to get a better location. Only 10 sites and again first come/first served so gauranteed to fill up fast. A bit further south is Manchester State Park which has a fairly large campground but gets much less use because no ocean view. Good luck.