It has never been easier or cheaper to buy your flight tickets. Most airline now follow a model in which ticket gets costlier as seats are booked. So it is always better to buy as soon as you can. Always check many sites to get the best fare. Check on master websites or even at the airline's own website. Here is a list for India. Scroll below to see all the sites.
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Air Costa and Air Pegasus are hard to depend on, cancel operations when in trouble.