THE ONLY TIME SHOWING UP UN-ANNOUNCED IS A GOOD THING
One of the more spontaneous things I've done in the spectrum of my whole trip was not planning out my hike to Macchu Picchu, considering the fact that my entire trip stemmed from wanting to hike to Macchu Picchu.
What I had read and heard from many travelers was to buy your hike in Cuzco. If you've got a little room to breathe time wise, I highly recommend booking in person with an agency, UNLESS you are going during peak season (July/August). Nothing wrong with online, but you can get much, much cheaper prices in person. I did the 5 Day / 4 Night Salkantay Hike (including meals, porters, guide, train ticket) and when I looked online, the cheapest I could find was $400. Prices ranged anywhere from $6-800 otherwise. When I arrived in Cuzco, and started walking around the different agencies...I saw prices starting at $230. Ya dig? And here's the clinger... everything is almost exactly the same! All the different agencies use more or less the same Trekking company. The trekking company in turn combines all the people from the different agencies into the same group. (Tour guides are freelance w/ KB Treks) You're on the same route. I ran into friends I met who paid more, on the exact same route, having the exact same food, doing mostly the exact same things! (FOOD is amazing by the way). The only difference is you pay for a smaller group, maybe a better sleeping bag and you have a porter for the very last day as well as opposed to carrying your own things the last day. (Not difficult) I was in a group of 10, and it was SO much fun getting to be with that variety of people.
I paid $300 for everything including walking sticks, sleeping bag rental + zip lining and a better train ticket and I had an amazing time. Sometimes there are a few differences, but nothing too significant that I think justifies paying $2-300 more. Click here to read more about my experience!