If you travel to South India from Europe, to Kerala, the best airlines in terms of price / quality is Qatar Airways. A roundtrip ticket, if purchased in advance, can cost between 400 € and 600 €. As France has political relations with Qatar, it is cheaper to travel from Paris to - Trivandrum (capital of Kerala, 70 kms from Varkala).
If you travel to North India, British Airways may be a good option. In any case, we recommend you do to your own research. For domestic flights in India there's several airlines: Kingfisher, Indigo Airlines, Spice Jet and Jet Airways and Indian Airlines. If you travel direct to Varkala, the nearest airport is Trivandrum International Airport. From the airport you can reach Varkala by car, train or bus. Takes 1 h to reach.
There is also Cochin Airport, that is served by Air Asia, which is a budget airline. From Cochin to Varkala, you can take a train (4h). After arriving to Varkala train/bus station, you can take a rickshaw (10 min, 80 to 100 Inr) to North Cliff, Shiva Garden Home Stay (next door to Akhil Resort, old Hotel Preeth).