Well, actually what Ryanair do is offer you a cheap, no-frills ticket from A to B, but then tell you that both the cheap tickets have been sold. You then have to buy an expensive, no-frills ticket from A-B, find that the return ticket B-A is twice the price of the one-way. You turn up at the airport and find that, if you actually get to B then your luggage (for which you had to pay extra because you omitted to inform them that you wanted your luggage to travel as well) is still at A and nobody from the airline is even prepared to talk to you, or they herd you onboard the aircraft, take off and then tell you that you're not actually going to B at all, but to C instead and that if you don't like it then you can just lump it. Ah well - at least you can buy a sandwich on board. Ummmm - no, sorry, you can't - they didn't take any catering upload and they've all been sold.
All true-life experiences - no disclaimer offered