SF
When you get back from your trip please update us on the real cost of the flight after you've been hit by any of the extras. Did you include the credit card charge in your £20 posted?
Will you be taking your own catering with you? and how far from your actual destination will you be when Ryanair deliver you? will you still need to pay out for a long coach/taxi (or car hire) to get you to your final destination?
Fair play to you if you can really do it for £20 per head or less, you can't argue with a bargain basement fare like that.