The price is inmaterial, but you must have paid something (valuable consideration). RYR then have a legal obligation to take from A to B. If they can't, they must inform you of your rights and then make further arrangements as appropriate. The EU rule is very easy to understand and can be read and/or downloaded from:
http://europa.eu.int/eur-lex/pri/en/...en00010007.pdf
However, it is also reasonable to wonder people pay as much as they do for "cheap" flights when often the "old" boys like BA and AF etc. operate similar routes (to the proper airports, not the renamed RYR jobs) often for lower prices, treat you as a customer and sort out the problems when they happen. Obviously, not all of the customers are pleased all of the time, but they have paid for they service and they will get it. And here is an example: A flight has to start from Metz/Nancy instead of Luxembourg due to the diversion of the inbound aircraft. Those passengers who could be re-routed from Luxembourg were, those who couldn't went to Metz. The airline provided the connection. Beer (etc.) and pretzels for all (part of the standard service). Those who were rescheduled for later flights went, and those who couldn't were provided with Hotels, meal vouchers and re-booked flights. The price of the ticket was not relevant - these people paid for a service and got one (eventually)!