Why not just get a decent Android tablet? My Nexus 7 has a great receiver in it. CoPilot Live is a great nav app. For amazing accuracy, (~3 ft.) I can use a GPS/GLO Bluetooth receiver with it.

I'm using a Garmin GLO GPS. It's a 10hz GPS, as opposed to the 1hz assisted GPS typically found in most Android devices:

http://www.amazon.com/Garmin-Portable-GLONASS-Receiver-Vehicle/dp/B00AYAZENY/ref=sr_1_3?ie=UTF8&qid=1417482915&sr=8-3&keywords=garmin+gps+bluetooth

It sits on the dashboard near the passenger-side A-pillar, with a mini USB cable there to power it. It has a battery, but it's not smart enough to turn itself on without pressing a button. The USB cable powers the GPS only when the car is running, which also happens to turn it on automatically.

I installed it because my Nexus 7 gets almost no GPS reception when installed in the dash. The bluetooth GPS seems to work well, except I had to cover the lights with electrical tape. They were way too bright.