The whole aftermarket car accessory thing is getting much cheaper, more advanced and, let's be honest, less cheesy. Gone are the days when you'd have to be a dab hand with a soldering iron and a spaghetti junction of electric wires to stick a two-inch screen to your dash with suction cups - and that's assuming you weren't required to cut into the dashboard with a hacksaw.
Plenty of in-dash DVD players are available these days that fit into any model of car in place of the radio head unit, and are easy to self-fit without ruining the entire dash fascia. Several look smart and come in a range of sizes, so it will slot handily into your car. It's not cheap at £250, but there's a range of styles for various budgets available here on Yahoo! Cars, so check it out if you're interested.