Dude, have you considered busting video monitors in the back headrests? That's relatively inexpensive. Or even better, buy one of those 7-10" portable DVD players and rig it up to your armrest in the center console. That way they can see everything that's going on and you can concentrate on driving. That's another cheap idea.
If you're still thinking about having it fold down from the ceiling. It's cool, but it's gonna cost you for sure.
If you're still thinking about having it fold down from the ceiling. It's cool, but it's gonna cost you for sure.