edi_local is correct in principle even if the amount he mentions is unrealistic.
Much as I detest RyanAir, everything he has stated is correct and valid. There's a simple choice, one I made long ago, I won't use them. All carriers have terms and conditions. Earlier this year I bought a ticket to SA on KLM, I went on their website, booked and paid for the cheapest ticket for my trip/dates.
While I was down there I wanted to extend my stay. I rang them and they asked me if I'd checked the fare conditions. I said no, I hadn't ....... they told me it was non-changeable. So I bought a new return ticket from SA which covered the southbound leg of my next journey. My fault, my problem, I still fly KLM and I don't go round slagging them off. And as someone's who's been in that side of the airline industry I know more about fares than most people so I should have been more careful.