MotionX GPS drive does have turn by turn but it is a $9.99/year add on. It is one of the reasons I went with the more expensive Tom Tom. As I said I got it on sale for $40 - so that is why I went with it. Also you can use Appshopper to monitor prices of apps.
App Shopper: TomTom U.S. & Canada (Navigation)
There is a iphone and ipad app which will notify you when an app changes (has an update, price increase, price decrease)
App Store - AppShopper