If you are backpacking around South America, the fastest way is to fly. We have student/youth fares on Taca Airlines which are much cheaper that flying as adult. There may be a long distance bus line, but if you are short on time it may be better to fly(and a lot less sketchy!!)

Brandon
Peru Expert
Berkeley, California
1-800-209-9083

No way by road is reasonably fast. Bite the bullet and fly, I promise you that it is worth it.