wich is the best way to start developing IOS app' s??

I am going to start developing in Swift as soon as I buy the new almost released MacBook Pro. Watch Jared Davidson's tutorials on youtube as well as "Let's Build That App". I like the latter better for more complex explanations.

Look up Stanford's iOS course (taught in Swift) on iTunes U. I've watched several semesters (from Obj-C days). He's thorough and comes up with projects that really teach you many frameworks available in the SDK.

Is there any truth in learning iOS is really expensive, because you have to pay for licences and stuff?

You have to have a Mac and if you develop an app you want to put up on the app store it's $99/year