I bought an Arkon IPM2-FSM 18.5-Inch Flexible Floor Mount for iPad 2
from Amazon for $35.
It mounts in about a minute to one of the passenger seat bolts (#30 Torx). I then bought MotionX GPS software for $4 and $20 for a year of Voice Navigation. It works fantastic. It uses the entire iPad screen so it is huge, downloads maps on the fly and uses Inrix for traffic data. I couldn't be happier with the setup.
When I have a passenger I am able to push the mount far enough to the center for the passenger to sit.