I wouldn't want to bug you but you know of the supposed bug with the cellular data tracking in iOS 6 right? Check it against what your carrier has listed for your line.... Only one can be right....Rather than bug us, why not find out?
Go to Settings -> General -> Usage -> Cellular Usage.
Note down the sent and received numbers.
Use navigation. When you get to where you're going, note down the numbers again.
Subtract. Now you know how much that navigation session used!
Given that it's all vector data, my guess is going to be "not much".