Yes, London travel is pretty expensive, but: You don't need a travelcard unless you travel more than once back and forth every days - pay as you go is cheaper. Also, the price of a flight without the airport tax is irrelevant, as there is no way to not pay it (which is why it's so dishonest for Ryanair not to include it in the price). Finally, commuting by bike in London is completely feasible - cycling from Poland is a significantly more substantial undertaking :)