Ok.. So here is my latest incarnation of an add-on headrest DVD player. I returned the Walmart branded one pictured above.
I got an RCA DRC630N Tablet style unit from Bestbuy. It is a DVD player and has 30 (lame) games. It came with a velcro style headrest bracket that the DVD player clips into (and removes from) very easily. I wanted something a little more permanent.
So I got a ProClip Headrest bracket with a Thumbscrew mount. This unit:
http://www.proclipusa.com/?sectionpath=107&pageid=9123
The RCA Main unit has a thumbscrew hole (the extra monitor does not). The screw was the correct size, but the RCA DVD was a little thicker then the monitor this was designed for. So I had to use a lighter, heat the bracket, and bend the bracket a little bit, so the hole for the mounting bracket and my monitor would fit.
I've attached a picture.
The DVD player was $135 after coupon (normally $149). The bracket was $70.