NAVIGON's new MyRegion is a customizable version of their turn-by-turn MobileNavigator app for iPhone that basically lets you buy just the navigation you need, when you need it, and expand via in-app purchase later.
Three "regions" are available in the US -- Western [iTunes link], Central [iTunes link], and Eastern [iTunes link]. Each region is currently on sale for $24.99 until April 12, at which point they'll be regularly priced at $29.99. Getting an additional region via in-app purchase will cost $12.99 on sale ($14.99 regularly).
NAVIGON MyRegion includes all the features and capabilities as MobileNavigator 1.4 plus NAVIGON MyRoutes. This new feature will be added to MobileNavigator North America via an upcoming update to 1.5.0 due this spring. NAVIGON MyRoutes is an industry first feature that learns from the users driving style to provide customized and better route recommendations. The feature also offers up to two alternative routes clearly displayed on a map including ETA, distance and driving time. This lets user choose the route that best serves their individual situation.
If you don't already have MobileNavigator and on-board maps are a must-have but not necessarily a have-all, give MyRegion a shot and let us know what you think!