California coast in the summertime and cheap do not go together - pick 2 of the 3. Often north of Ventura the worst months to be along the coast are July and August unless you like maritime overcast days and lots of wind. The coldest month is February and it gets warmer month by month to a peak in September and this last month is the best time to be in California or in May. Better weather, fewer tourists, and off-season rates.
Lots of state parks with senior rates and also BLM lands and county and city RV parks that are more difficult to find but will have great rates. There are campgrounds that are first come first serve so if you arrive by noon you have an excellent chance of finding a space.
