I use a TomTom GO520 on tours, I bought it last summer for our USA vacation, it cost 200€ and was cheaper than a navigation system in a rental car for the holiday season. It has the advantage that all maps of the whole world are included and that it makes free updates of the maps. It has its own Wifi and makes updates independently of the PC. With the MyDrive app you can plan the whole vacation on the PC with comfort and then you send it to the TomTom easily.
It has one big advantage: It guides the route you want to take, as you have entered it. Smartphone applications like GoogleMaps dynamically change the route as you drive. You want to drive through the nature park, but because another way is shorter or faster, you suddenly drive past garbage cans, slums and scrap yards with Google Maps.
Michael's recommendation sounds good when you use a smartphone, Motomappers.
BTW, „Here“ is an invention of Nokia, later on, German Car builder have bought this system. Beware, „Here“ also changes routes during driving.
