Headrest DVD players - recommendations

My youngest son is now at the age where he needs some entertainment in the car during long journeys. I currently have a single headrest DVD player which has worked wonders for the eldest but now I need to have two units. I was hoping to get some recommendations for models that would allow the two players to play different DVDs simultaneously. I bought a set off eBay a few months back which were complete headrest replacements however these didnt fit will and rattled very slightly in the seat so they had to go back. I don't mind having the players strapped on to the headrests and I don't mind using the cigarette lighter to power the units however if I could get away from both of these constraints I would be very happy. My main issue would be price though. I am hoping to do this under £200 if possible. Any suggestions?
Thanks
Allan

If you're comfortable converting your DVDs to MP4 files (I use Handbrake) then you may want instead to look at the likes of the Nexus 7 tablet. It fits your price point and would be good for 10+ hours of programs even without hooking it up to power. With a little tweaking you should be able to get over 20 hours of different programs on the 16 GB unit.