I always find it hard to find cheap flights for holidays but a friend of mine has a site that helps:

Creating your own "do it yourself" holiday just got a lot easier with diytravel.co.uk's new flight search. Search low-cost airlines (including easyJet, Ryanair, BMI baby, Thomson Fly, XL, flybe, Jet2), scheduled airlines (Virgin, British Airways, KLM etc) and online travel agencies (Expedia, Opodo, ebookers, Travelocity and lots more) to find the cheapest flights for your trip. The diytravel.co.uk flight search system is free to use and no service charges are added on to the ticket price - you buy your tickets directly from the airline at the airlines normal price. Check it out here

It's worth a look! and remember when flying go carbon neutral.