Where a card says pay, that indicates a cost (except for "Gishki Photomirror"). "Imperial Order" is a good example of this.

However, with Spell Cards that require you to pay in Life Points (e.g. "Dimension Fusion", "Brain Control", "Premature Burial", "Final Countdown", etc.), this can be bypassed with "Spell Economics".

The Life Points paid for card effects don't count as damage inflicted to the Player or taken by the Player. For example, if you activate "Rainbow Life" and then pay 4000 Life Points for "Wall of Revealing Light", you won't regain the Life Points because they aren't damage but the cost to play "Wall of Revealing Light".