Hi @quantumodo,
Thank you for your response. However, the rule you provided only states that you should resolve the effect after paying the cost; it does not clarify whether you should select the targets of that ability before or after paying.
After giving it considerable thought, I still believe that targets should be selected before payment. For example, consider a card that reads:
Action: Shuffle each card in your discard pile into your deck.
You cannot trigger this card if you have no cards in your discard pile, even if you can discard cards to pay for it.
If you have any differing opinions or insights, I would love to hear them.