Dana Point is one of the nicest place in California but also one of the most expensive (as I'm sure you know!) - assume you've tried looking a few miles in surrounding areas to see if you can get something close but a bit cheaper?
Cheapest guaranteed way to fly right now is Norwegian from Gatwick to LAX - can get it for under 200-300 GBP each way. They are pretty set as long as you book far enough out... but like Bozza says, depending on what time of year you can get BA/Virgin flights for the same price, but likely not at...