There are many options to consider with a DVD headrest install. Many units that are already assembled (like the OEM ones) will have the DVD players built right in. This will allow two separate videos to be played at the same time. Others, which sounds more like what you are looking for, are just a screen, and require a separate DVD player as a source (like the radio head unit).
You can get anything you want with the right amount of money. Even installing your own screen can get expensive if you want something nice. Here are some of the things to consider -
1. Vizualogic offered a nice option that was just the screens installed in, and factory matched to the vehicle headrests. It appears the product has been discontinued at Crutchfield, but a seller on eBay still has a listing
HERE.
2. Another route is this eBay seller
HERE. They offer factory matched headrests (colors and material) as well. Only, these screens are offered not only as DVD players, but are also touch screens. They seem pretty nice, but unfortunately come at a cost.
3. This is probably the cheapest option, but installing your own screens will require some DIY work. The best thing to do is to watch videos on how others do this. I will provide some links -
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How to Install Headrest TV's Part 1
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How to Install Headrest Tv's Part 2
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How to Install Headrest Tv's Part 3
Of course, this all requires that you have a screen to install, and a headrest to work with. If you go this route, I would highly suggest that you purchase extra headrests to do the install on so you don't ruin your factory ones. Finding a screen can be as simple as doing a google search, but a decent one I have come across, and one that doesn't cost a great deal of money, is made by Clarion. The Amazon product page is located
HERE.
I know that is a lot of information, but there is much to consider here. I would suggest that you also check eBay and Craigslist. You just may find a great deal. When I was looking I considered all of these options, but ended up finding a pair of OEM headrests with the built in DVD players for just over $300.00. I couldn't pass up that deal, especially considering that they were the cashmere leather that I have in my Tahoe. I hope that helps! Feel free to ask questions if you have any. Good Luck!!