India is a country where you can live like a fakir or like a Maharaja. Travelling expenses could be varying depending on your needs and desires.
If you are planning to stay in cheap hotels, travel II class all the way and live on rice and dhal, you will be able to see India on a daily expenditure of US dollar 50-60.
If you are looking for a better accommodation (a room with attached bath), eat a varied diet and willing to spend occationally on I class or AC long distance train journey, it will cost you US dollar 100-120 a day.
If you want to stay in mid range hotels, eat in decent restaurants, always travel first class and engage occasional car with driver, the expenses will be about US dollar 150-200/day.
If you are looking for the best five star facilities and plan to stay in converted Maharaja's Palaces and live five star, then you can budget the travel as if you are travelling in the west.