Depending on when in May you're thinking of going you may find that cheap fares won't be as easily available as they were last year. Last year virtually the entire month of May was off-peak because Ascension Day fell at the very end of May and Pentecost was in June. This year Ascension Day is on 6 May and the Pentecost public holiday is on 16 May which means that a lot of people will be travelling in the first three weeks of May.