There are plenty of companies that give guided tours of the Salkantay Trek. I went with Machu Picchu Reservations and felt like it was great value for the money. The hike is 5 days/4nights through the most stunning scenery. The demographic of the group was mainly backpackers or 35 and under. It's one of the cheapest tours which is why it attracts this type of group.

The $270 USD price includes the tour guide, 3 hot meals a day, accomodation, transportation, and the Machu Picchu entrance/tour.

Other companies are more expensive but include even nicer accomodation, transport, and food. I personally felt like all the above were perfectly acceptable but of course if you want to treat yourself a bit then go for a different company.

You can also do this trek without a tour. Plenty of people set off on their own or with their own group and stay in the little accomodations along the way. You can also camp but then you need to carry your gear. You can buy food there and pack a lunch. It's much more affordable than the tours but you do need to sort your own transportation to the starting point and back to Cusco.