It's been five years since I last transported a bicycle by plane and the escalation in charges is pretty horrific. Our friends Ryanair top the list for rip off charges with a heft £50 fee for each leg of the journey. That will add £100 to a return journey; you could buy a cheap bike abroad for that kind of money.
Easyjet is a little better with a £25 each way fee whilst British Airways gets my vote for its free of charge carriage of bicycles.
Taking a bike with you can make life a lot easier. You can reassemble it at the airport and start your journey straight away. This is great at Ibiza airport where you can ride into unspoilt countryside within a few minutes of departing the airport.
It is also great to have your own bicycle with you rather than a hire bike. My beloved Thorn tourer is very well travelled.