TRAVELLING INDIA- tips on spending?

Travelling India for a month or two is definitely up there on next years list. However, being a student I won't be flushed with cash. I will have about 500-1000 pounds to spend, of course living in cheap accommodation, doing a couple of weeks voluntary week and travelling the country by public transport. I will not always be in the most tourist places though do want to see Pondicherry, Agra, and Mumbai. SO, with the current climate is it possible? Or do I have to aim to be there for less time. Any tips would be appreciated. I have also read on the internet but thought it might be useful to ask Natives, travellers or anyone else in the world. Thank you!