About how much would it cost to fly from California to Britain?

Ticket prices vary a lot depending on when you're travelling and how far in advance you buy your tickets. If you expect to spend $2000 you shouldn't be unpleasantly surprised if you buy your tickets three weeks in advance.

You can get specific prices for specific flights between any two commercial airports from google, and I strongly recommend that rather than relying on a general statement like the one above. I've put a link in the related links section.