There are other airlines that fly between Santiago de Compostela and Barcelona. Try Vueling and Clickair (Spanish low-cost airlines), whose fares start at €35 one-way. I've never flown with them, nor do I know anyone who has, but I doubt they can be any more dispiriting to fly with than Ryanair.
(Sorry... I misread the original post and thought you were trying to get to either Santiago de Compostela or Barcelona from London)