I spent around 3 hours today on this mission and a few attempts on another day. Tough mission. One thing that helps is going to the airport immediately and killing everything, shooting down the planes before they take off. Also going into the tunnels and shooting the parked planes. You cant auto target them but you can machine gun them and kill them with non locked on missles. Those planes seem to be worth 1k each or so.
Failed attempts edited out. This mission has no checkpoints. Once I hit the target score I was just trying to survive the last 2 minutes, which was tense.