There is an added, but necessary, cost hiding in every trip, or vacation that one takes and that is travel insurance, or the insurance taken out when traveling. It is hidden because it is one of those costs that needs a separate question after you have already arranged all the other details for the rental car, or the airlines you are traveling on. The question of whether or not insurance should be procured almost seems to be an after thought, but it is definitely an important part of any trip, and probably adds a good 10% onto the cost of the trip.
