Car hire in California is much more expensive now than it was pre-pandemic. Even small cars are $35+ per day now, and they aren't the sort of cars you could drive long distances with people and luggage. For a decent size car you are going to pay $50 - $60 per day. Gas is $4.20 per gallon.
Decent hotels are seriously expensive too. In LA or SF you need to budget at $300 per night. Of course it'll be cheaper outside of big cities. Food and drink is entirely what you want to spend - from $5 for a burger and coke in Rotten Ronnies to $500 for high end dining with wine in SF or LA.
I know the temptation to cram in as much as you can in two weeks but California is almost twice the size of Britain. If you try to do too much you just spend two weeks in the car driving. Two weeks is just enough to explore LA, drive up Route 1 and explore SF. Don't try to cram in Las Vegas or Death Valley as well. Route 1 - it's just a two lane road for most of the way. Don't try it any weekend from March to November, or public holidays, or any time at all in June or July. It just grinds to a halt at every town on the route, you can't even average 30 mph except in the middle of the night, and there's no point in going on it in the middle of the night.
I'm not trying to put anyone off a driving holiday in CA because it's one of THE great places but you have to be realistic about it. Spend more time exploring places and less time driving and you'll have a much better holiday.