This goes double for a country like India where choosing a tour agency to arrange your trip can make a huge difference in terms of cost and quality of service.
For instance, the search option "tour operator Shimla" would provide you details of tour operators who deal only with Shimla and other destinations in the northern India.
Some ask for upfront fees and then keep asking for more money at regular intervals during the trip. So make sure you ask the tour operator to break down the costs and explain the details pertaining to the same before the trip.