Now you're REALLY talking boondocks! They don't call it "The Lost Coast" for nothing.
I don't think you have any choice whatsoever in Shelter Cove proper (there MIGHT be one restaurant out there).
Redway and Garberville are your next best bets, but they are about 20 miles from Shelter Cove and they have very limited options as well.
The Benbow Inn is the nearest I can recommend and it's pricey.
I have a friend who still lives out there, I will ask him next time we talk if they've got any new prospects.
My advice--bring a picnic.
Also the Brass Rail in Garberville has decent dining options. Lamb chops and Prime rib style dinner house, serving cocktails, located next to a clean, ok motel, run by the same folks. It's an older, rancher dinner house, white bread rolls, crudites. Dark interiors, but a local institution.