Camping in California or any state doesn't have to be expensive. We were full-timers for 16 years and traveled constantly, including Alaska.
If we had to pay for a full hookup RV park for our every stay we could not have traveled like we did. That's 5,840 nights.
There are many ways to do it with low cost. Yes JimK-NY :) even with our 40' motorhome and slides we did not utilize RV parks with full hookups. We didn't need them so I don't know where you got the idea that big rigs do. You keep repeating that statement.
We stayed in awesome boondocking spots on public lands. (national forests and BLM). We also stayed in forest service campgrounds, national parks, state parks, COE, county and city parks. The majority of time without hookups.
Site costs depends only on what you think you need. You can get by a lot cheaper in much more beautiful surroundings if you use public areas/parks. We had a built-in generator but used our solar panels - nice and quiet.