are you looking to do it yourself? or have a shop build and install one for you?

when i played the carputer game i picked up most of my parts off of Mp3Car Custom Car Computers! every now and then they run a deal for a total package where all you need to do is load your os and go for cheap money.

they are fun, you will run into kinks, they will piss you off but when it works it is a very cool toy

::edit::
just re read and noticed you want to have a shop do it for you, it's easy do it yourself lol