Let me ask you a question, do you have to discard either fire or electric energy to use Rayquaza EX's second attack? If you say yes that is my example and explains that cost and effect are pretty much the same thing and one cannot be done without the other. If you said no, prize to you're opponent you're turn ends before you get to attack.
Yes, you do have to discard Fire or Electric basic Energy. But your example isn't an example of a cost, because even if I have two Prism Energy on Rayquaza, it doesn't stop me from beginning to use the attack.