Quite interesting that they say:
"FLY DIRECT FROM OXFORD AIRPORT TO PALMA, MALLORCA – and what’s more do it in style and comfort...and at a price that will often work out cheaper than flying with the ‘no-frills’ airlines or other charter flights."
So I've tried to see what Monarch have to offer for a week to PMI from LTN out 06Aug for a week. The highest price I can get with bags/meals/extra legroom seats/lounge/a bottle of champagne out and back is £380.96...yet their lowest guide price for August departures is £550.....
Gonna have to do better than that!