Finding cheap flights to Marseille from other cities is easy. Low-cost carriers like easyJet and Ryanair offer plenty of cheap flights to Marseille Provence Airport (Aeroport de Marseille Provence), especially if you book well in advance.
Here is a list of low-cost airlines that fly to Marseille Airport (MRS), and the cities that they fly from:
Aer Lingus has flights to Marseille from Dublin
Aigle Azur has flights to Marseille from Algiers, Annaba, Bejaia, Chlef, Constantine, Oran, Setif, Tlemcen
Air Mediterranee has flights to Marseille from Bodrum, Dakar, Djerba, Dubrovnik, Heraklion, Ibiza, Marrakech, Monastir, Split
Air Transat has flights to Marseille from Montreal (Trudeau), Quebec City
Blue1 has flights to Marseille from Helsinki
easyJet has flights to Marseille from Bristol, London (Gatwick)
Freebird Airlines has flights to Marseille from Antalya, Istanbul (Ataturk)
Jetairfly has flights to Marseille from Agadir, Casablanca, Marrakech
Norwegian Air Shuttle has flights to Marseille from Copenhagen, London (Gatwick)
Pegasus Airlines has flights to Marseille from Istanbul (Sabiha Gokcen)
Ryanair has flights to Marseille from Agadir, Bordeaux, Brest, Brussels (South Charleroi), Cagliari, Chania, Dublin, East Midlands/Nottingham, Edinburgh, Eindhoven, Fez, Gothenburg (City), Groningen, Ibiza, Lille, London (Stansted), Madrid, Malaga, Malta, Marrakech, Nador, Nantes, Palermo, Paris (Beauvais), Porto, Rome (Ciampino), Seville, Stockholm (Skavsta), Tangier, Tours, Valencia, Warsaw (Modlin), Weeze, Zadar
Sky Airlines has flights to Marseille from Antalya
Syphax Airlines has flights to Marseille from Sfax
Twin Jet has flights to Marseille from Basel/Mulhouse, Geneva, Metz/Nancy, Pau, Limoges
Vueling has flights to Marseille from Barcelona
XL Airways France has flights to Marseille from New York (JFK), Saint-Denis de la Reunion