you can do it much cheaper than that, and personally linux isn't the best for mobile because there aren't many apps for it. I just helped one of the guys at my work write a gui in VB for his car PC. Real Easy. I'm not sure you'd want to go as nutso as he did, but it was in a olds bravada, so you might not have the room he did. He put 10" SVGA Monitor on a flipdown mount, he used this as the base
http://www.thinkgeek.com/computing/handhelds/5a98 then added an usb wireless NIC and GPS module, usb fm/tv tuner, sound blaster extigy goes right to his amps, has a backup cam tapped into the capture port on his tuner module, changed the HD to an 80gig he found a little plate and added extender cables for a nice adapter plate for the firewire and usb ports and video in. All in all I think he spent $2500 including software for one badass car toy, does dvds, mp3s, when he pulls into his garage it syncs with his home network, it has auto routing navigation, voice prompting, and so many other features it's not even funny. The only thing I would have done different is used a touch screen. The coolest thing I've seen with it was we were listening to some tunes, one of the guys in the truck said damn dude, that's a wicked song. My friend pulled over and burned a cd for the guy lol.
I was looking at using the same PC he did with a 7" 800x 600 LCD with touch(I can get for $500), and since I'm somewhat of a visual basic guru, I could make a bad ass gui to run everything. I've even found some USB relay pods and analog out pods, so I could control stuff like the windows, locks, climate control. Just wish I had more damn time, it really wouldn't be that expensive.