Go through your results for flights to Patna in India with Netflights.
If these flights are too expensive, try searching for a different time of year. So if your dates are flexible, consider looking at different times of year.
Or broaden your search by looking at other airports in India.
For even more options, check what other airports you could fly to Patna from. You might be able to make a saving by going from a different airport or city.