Shit, this makes me want to build a m-ITX computer and shove it on my dash!
I just dropped 2.5k$ on my last build, i cant afford another haha
If you need help figuring out components to build one yourself, just ask! An older sandy-bridge CPU, m-ITX mobo, 2-4GB RAM, and a small SSD (or HDD if you can fit one) would work great. Im not sure what monitor you would go with though... Also, you might be able to modify a PSU so that you dont need an AC converter at all, although im no expert in that regard.