I'm an American that travels somewhat regularly overseas (usually S. America and Europe) as well as a bit in the US. Generally when I rent a car I just add a navigation system. So far that has worked well, but I'm concerned if I ever end up in a spot where there isn't one available, and also that I am wasting money.

So I'm thinking of getting a navigation system, preferably a cheap and simple one that won't get me lost (the Hertz system I have rented a few times is perfect). I'm just worried that:
--I will end up in a place unable to get a signal (this could be unpleasant in a country where I don't speak the language, and in the US happens all the time with my phone navigation system)
--the maps are not up to date or useful

Does anyone have any tips so I can avoid those pitfalls? And also, any tips on how much I should spend are helpful--I really don't need any bells and whistles with this thing.