I was planing on doing this with a Nook Color ($200+import postage).
It would become my mobile computer/entertainment (displacing my smartphone and "notbook") as well as the car's central.
But now I can grab the Galaxy Tab (way better) for only $299 ...but theres no custom ROMs for it.

If those costs are too high for some of you, then even the simplest Android tablets (Apad?) could be something good for the centre console ...but definitely not a good mobile computer.
Have a look around at this site:
http://www.wholesaleonepiece.com/Who...&productsort=4
or
http://www.china-tablet-pc.com/andro...t-pc-c-14.html