I suggest you have a look at the latest iPad headrest mounts. If the Ford Invision system is $2000, you could cut that in half by buying two iPads and the mounts. Download the movies on iTunes or some other program and forget about having to pack around the DVD case.
Plus the iPad screen is bigger.
Also if you look at SYNC functionality with the WiFi options using your cell-phone data by USB tethering, your occupants can surf the web while you drive.