I traveled in India from the 16th of November 2005 to the 1st of March 2006 which is 3 and a half months.
At first I was supposed to leave the country on the 1st of February but hey India is so big and there is so many things to see that I finally staid one more month.
In addition I had to stay about 10 days in Mumbai because of a tooth root canal infection and I spent 10 days in a monastery as a Buddhist monk.
I did a round trip from Delhi to Delhi clockwise.
Here are the places I went (in chronological order, a long list !):
Delhi, Agra, Gwalior, Khajuraho, Varanasi, Calcutta, Darjeeling, Bhubaneswar, Konark, Chennai, Pondicherry, Madurai, the Keralan Backwaters, Kochi, Mysore, Hampi, Panaji (Goa), Old Goa, Arambol (Goa), Mumbai and around, Aurangabad (lost the pictures... and my camera), Ajanta Caves, Ellora Caves, Daulataba, Amhedabad, Palitana, Diu, Junagadh, Udaipur, Ranakpur, Kumbhalgarh, Mount Abu and Dilwara temples, Jodhpur, Pushkar, Bundi, Jaipur, Amber, Bikaner, Jaislamer, the Great Desert of Thar, Amritsar, Mc Leod Ganj.
I usually spend no more than 2 or 3 days on each place otherwise I got bored!
About transports I mostly used trains (in Sleeper or 2d Class) or buses when there was no train or when it was more convenient. For long distance buses I tried to take private ones as much as I could as they are much better than the government ones.
I slept in cheap hostel from 100 to 250 Rs for one night in a room sometimes including bathroom sometimes no.
Food was cheap and a meal cost me between 20 Rs (for a basic thai) to 120 Rs (already a good meal). I can't deny that at the end I spend a few more bucks for food.
I also bought some souvenirs and had some unplanned spending like a new teeth (root canal infection) and a new camera (I lost the first one) both quite expensive by Indian standards.
I planned to spend 20 euros a day which is large. I had a total budget (transports, hostels food, monuments, souvenirs...) of 1500 euros for two and a half months.
Actually in three and a half month I only spent 1621 euros which is 15.3 euros a day. So it might seems a lot but not that much considering I moved a lot (trains and buses end to be expensive).
In addition I had this tooth problem (7000 Rs) and had to buy a new camera (10400 Rs!). I also bought new glasses (850 Rs only !).
Finally my opinion is the same as many other travellers' one who've been there: India, sometimes you love it, sometimes you hate it!