Life-long Orange County resident here - Check out:
- Newport Dunes in Newport Beach - the have long-term rates posted on their site and depending traffic, you'll be about 15 minutes from the airport. This is tied to a beautiful, 5-star resort area, so you'll have all kinds of services available (parking, laundry etc.)
- OC Fair and Event Center: Yes, you can camp at the fairgrounds, and for not a lot of money. Close to Irvine as well. They close the camp area for large events, and the OC Fair is going on right now...
- O'Neil or other county parks. They have a stay-limit, but are inexpensive and could be a good bet if you don't have a place picked out when you arrive.
While there is gang activity in certain spots, I think you'll find most areas to be pretty decent. I've never had any issues with the unsavory elements, even working in the heart of downtown Santa Ana.
Like BigBaron says, Google's probably going to be your friend, but feel free to post back to this thread with questions as you have them. I've lived here for a loooong time and would be happy to share what I know.