We have a relatively new Garmin 2757LM ($220) that comes standard with all of North America but I do not know if any Garmin has Central and/or South America. The new Garmins do much more than the older ones and in our opinion are worth the investment. As stated above no GPS is perfect so having one you can plan and route and see the entire route before setting out is important. Older models are not as accurate. Best to get on the Garmin website to find answers to your questions. I personally do not know of a GPS for South America but they may exist. We also use Microsoft Streets & Trips in our computer to plan routes and can also be used as a GPS if you have room for it. But even S&T does not have South America - but Microsoft does have another mapping software product for Europe. There may be other software we do not know about. One place to look and ask is . . . www.laptopgpsworld.com . . . where tons of info can be found and there are forums there where you can ask the experts. We find modern GPS to be much better and more accurate than any paper map we are aware of. There is another current thread going here about S&T that may be useful.
I personally know nothing about any of these.
Try this Garmin web page...........
https://buy.garmin.com/en-US/US/maps/on-the-road-maps/city-navigator-nt/city-navigator-sup-sup-south-america-nt/prod98712.html
Other possibilities.....
http://www.gpstravelmaps.com/central_america.php
http://forums.gpsreview.net/discussion/11870/which-garmin-to-use-for-central-america/p1