Mark David Blockbuster filmmaker James Cameron, whose films have grossed an astonishing $6 billion in worldwide box office, has hung a $25 million price tag on his sprawling, two-mansion compound in Malibu’s discreet and reclusive Serra Retreat enclave.The “Avatar” franchise writer/producer/director, who earned three Oscars for the 1997 film “Titanic,” acquired the first property for $3.475 million in 1989, around the time he married his third wife, Oscar winning filmmaker Kathryn Bigelow.