GPS is pretty much a gadget out of Buenos Aires. This is a big country with few inhabitants. As a matter of fact, there arent too many villages, like in Europe, and roads are long and straight, very visible and identifyable on a paper map.
The same logic applies to Chile.
Unless you want to follow others travellers waypoints, there isnt much point in using one of those at those latitudes.
Better spend your cash on tyres and warm clothes. You will have a lot of wind on Route 40 down south.
Don t forget to leave a gift on
Difunta Correa shrines so that she protects you from road hazards.
Here is a website where you could find usefull informations. We had a couple of canadians here travelling with a 4WD that found all their informations there :
http://www.horizonsunlimited.com/hubb/