If you won't be using the maps all that often, and you are renting a car, you may want to consider pricing out renting a GPS with the vehicle. Just another option.

It may also be less expensive to pick up another GPS with the proper maps loaded on already for less then buying the maps.

If you will be going back to europe enough it may be worth to just buy the map, but I would have a hard time spending $300 on a map when I can buy an entire GPS with the maps loaded for way less.