The only advice I can provide is on Brazil. I've spent a lot of time between Rio and São Paulo. You can grab a bus or rent a car in Rio or São Paulo and head to the coast. The coastline between Rio and São Paulo is beautiful and there is plenty to do without getting stuck in tourist traps. There are lots of cheap campgrounds with good amenities, white water rafting near Ubatuba and many beaches to hike to that are far off the beaten path. Most of the cost between the two cities is mountains that run right up to the ocean which creates some amazing views and little beaches tucked in between where the ocean meets the mountains. I have three photos from near Ubatuba posted in the photo galleries
http://www.365adventure.com/photos/s...ry.php/cat/504 and I'll try to post some more next week.
The only other places I've been in Central/South America is Honduras. I went to Roatan which is one of the Bay Islands off the coast. I didn't really doing anything there besides scuba diving but the diving there is amazing! Photos from Roatan (mostly underwater because that's where I spent most of my time in Honduras
):
http://www.365adventure.com/photos/s...ry.php/cat/501
Hope some of this is helpful in your planning and safe travels!