They charge $20 if your wheels touch the pavement.
I agree about CMA... the airport cafe is excellent! I recommend the open face turkey sandwich - in fact if my wife weren't sick today, I'd head down there with her on a date and get one right now for dinner.
Heading down to San Diego you should REALLY take the mini route - it's 2500' over LAX. It's kind of intimidating even for locals - especially their first time so here's what you do: when you depart VNY ask for freq switch to SMO tower - tell SMO tower that you are coming over the pass, (which is the 405 freeway through the hills - look for a circular white building in the middle, that's the 'Getty') your type aircraft, and you want clearance through the mini route, tell them your destination - they will call LAX tower and help coordinate. SMO will get you your squawk and give you a freq change. When you call LAX tower let them know that you are ~3 south of SMO - or wherever you are - for the mini route. Don't enter the B unless you get a clearance (although, there is NO radar coverage @ 2500' due to radar clutter) and fly over LAX @ 2500 feet. They only let one person in at a time, so you might have to do a couple of turns around the marina, no big deal, Venice beach is right below you, and it is mighty cool. When through, ask for a freq for SoCal and get flight following to San Diego... take the coast, watch out for the area around Camp Pendleton, and have fun.
Attached are some (older, from '05) pics to help convince you.
