Having used both systems before I really like the intalled dvd players so much better. When we bought our last car I called around for an after market system. I think most of the stores/dealers were like $ 600-900. I found a guy that my dealer uses to install them and it was only $250. So it can vary greatly but if you can find someone who does it on the side it will be so much cheaper. I also had them install a button so that when we want to listen to the radio the kids can still listen to the dvd player through headphones.
DS 2005
DD 2007
DS 2010
and a Junebug in 2013