The best place to book a hotel would be dependant entirely on what you are aiming to achieve from this trip. If you want to stay close to the main areas and markets. We would suggest you to stay at the Mall Road. Otherwise there are nice places near Aloe and Hadimba where you can get good hotels.
There is a hostel culture too in Manali and those who are looking backpacking can get a lot of Hostels and backpacker places.
Per person, the stay should cost you Rs. 700 -800 on an average. It can go up to 1000 and more if you are looking at a costlier hotel. If you are travelling with family, we would suggest you stay near the Mall Road.