$2500 for a rear entertainment system in the Honda Odyssey? No thanks. I spent $100 on components to build a movie server out of a router. Power is switched to the car ignition and the router is plugged directly to the DC power outlet (no inverter required).
The Netgear WNDR 3700 router runs DD-WRT Linux firmware and serves movies via the HTTP and DLNA protocols. It also serves music via the DLNA protocol. Movies and music are stored on an attached USB hard drive. I wrote a script that builds an html file with all of the movies linked to the displayed cover art. This will allow a user to stream a movie without any special software.
The kids seamlessly browse movies stored locally on the Kindle Fire, as well as movies stored on the server, using the "MovieGallery" app, sold in the Kindle and Google app store. Music is served to the factory Honda head unit using Bluetooth streaming from a smartphone, which is attached to the router via Wi-Fi and pulling the music using the "BubbleUPnP" app (works via DLNA; also on the Kindle and Google app store).
The router is tucked into the nook in the trunk area of the Honda Odyssey. I created a cable that has the router power plug on one side and the power outplet plug on the other side. No inverter is required. The WNDR 3700 has a voltage regulator that can accept all voltages the the car may produce (11V-14V). I have a two-outlet power adapter that also has two USB charging ports. One power plug goes to the router, one USB charger goes to the hard drive, and a second USB charger is used to charge the Kindle (a cord is neatly run from the nook area to where my son's car seat is located).
Step 1: Purchase Components
Purchase a used Netgear WNDR 3700 V1 or V2 from Ebay ($40-ish, delivered). Also purchase a used (or new) USB powered hard drive. 750 GB is plenty to store a couple hundred movies.
Purchase a multi-use vehicle power adapter/charger. You are mainly looking for a two-port USB charger. The one I purchased is below:
Step 2: Flash Router
Flash DD-WRT onto the router. then install Optware, an lighttp, and minidlna. I wrote a detailed tutorial at:
Step 3: Build Power Cable
Build a power cable. Radio Shack has universal 12V power cables which you can purchase a tip to match the power plug on the router. I took an old power supply that had the correct tip, cut the cable, then installed it into a 12V power plug clam shell. Make sure you have a fuse somewhere in the power delivery.
Step 4: Install Into Vehicle
Unless you are installing into a Honda Odyssey, chances are you will have to get creative with a location to house the system, and a switched power outlet. It's crucial you supply the router with switched power to ensure it does not drain your batteries. My original intention was to install the router behind a trim panel.