South American Flights`

Hey folks, just curious if anyone here has any experience catching flights in South America. I've briefly looked around online, just seeing what's available, what I can expect for costs, etc, but haven't found a lot outside of stuff like expedia.com and other travel package type sites. We're considering a single flight just to save time from Rio Brazil to Peru so we can do the machu picchu trek. Any estimates on what we should expect to pay?? Thanks as always, we're just over 80 days away from departing!!!! : )