Yep its Ryanair. It really depends on when you book them. If you book early they are normally 40 quid max, mostly tax charges. If you chance it and wait until closer the time and offers may come up, thats how I got to the West Ham game in December, and now for the Arsenal and Spurs games.
Ryanair are a bastard for tax charges. On their front page they will offer you flights for so little but their tax charges more than make up for the loss.