The only people who do not need a visa to travel to India are citizens of Nepal and Bhutan. Otherwise, all travelers from outside of India will need a visa to visit the country. How much you pay for your visa depends on your country of origin, but you can easily apply for a visa online on the Indian government's website.
It's recommended to view your country's India International Travel Information page for the most up-to-date information on entry and exit requirements -- including visa information -- for foreign citizens. You can also contact the Embassy of India.