Getting an India Visa is relatively easy. You can search for the web site of the Indian Embassy in your country, which will have the relevant details and downloadable forms. This should be done well in advance (4-6 weeks) especially if you are sending it by mail. The cost of the visa varies by country as does the length of the visas available. A six month tourist visa ($60) is adequate, though over time it may save money to apply for a five or ten year visa ($150, available in the US, may not be elsewhere). All tourist visas begin on the day of issue (not the day you enter India). For all tourist visas, the maximum period of stay in India is limited to 6 months (180 days). Visas which are valid for over 180 days (i.e. anything but a 6 month tourist visa) say that you must register with the Foreigner Registration Office within two weeks of your arrival in India. In practice however, you probably don't need to do this if you are only staying for a month.
Getting a Visa