First of all, my first advice to you is: DO NOT BOOK THIS TREK FROM HOME! Do yourself a favour and save some money... There are PLENTY of travel agencies all around Cusco, Lima and Paracas where you can buy the trek. I would suggest you buy it a few days in advance to make sure you have an entrance ticket for Machu Picchu and a train ticket from Ollaytambo to Cusco! There are daily departures for this trek. There is no reason for you to pay tremendous amounts of money.
Just to give you an example... We booked the 5D/4N trek while we were in Paracas on June 4. We paid $300 US at Emotion Tour. The owner there arranged everything and gave us the tour operator number. When we arrived in Cusco, we called the operator and arranged for a briefing day. The trek started on June 9. We had a nice hostel in Aguas Caliente, an entrance ticket to Machu Picchu and a train back to Cusco from Aguas Caliente at 6:30 pm. We were quite a large group but had so much fun. I know some people prefer smaller group but it is hit or miss. It seemed to me that people pay different travel agencies and these agencies deal with a few tour operators. Our tour operator was Arsa. The guides were friendly and seemed to enjoy their jobs. The food was very good and the cooks made sure it was cooked according to "western standards".
While we were on the trek, some people in our group told us they had booked the trek from home (USA and Europe) and paid between $600 to $800!!!! Someone is making money somewhere. That is to say that I emailed a few Peruvian tour companies while I was still in Canada planning our trip and received quotes of $700 and sometimes $900! and these were tour companies recommended by Lonely Planet. I am so glad we took the chance and waited to be in Peru. We received the same service as everyone else on the trek. The money doesn't go to the guides... I bet you if you email Emotion Tour in Paracas from your home country, they will arrange the trek for you.
Also, we recommend you do the 5D/4N rather than 4D/3N. The only difference between the two was that you get a free afternoon in Santa Teresa where you can go to the hot springs (amazing site) and a free morning where you can go zipling.
Included: food, horses who carried our bags, tents (and set up for us), mattresses, guides, Machu Picchu entrance ticket, train from Aguas Caliente to Ollaytambo, bus from Ollaytambo to Cusco. Not included: sleeping bag (I rented one in Cusco. I paid 70 soles for five days), water (you can buy supply along the way), bus from Aguas Caliente to Machu Picchu (15 min bus ride.. you can hike it up if you'd prefer), hot springs in Santa Teresa.
If you want more information, don't hesitate to contact me!