If unbound, it's still
technically successfully cast:
Age of Sigmar Core Rules wrote:To cast a spell, roll two dice. If the total is equal to or greater than the casting value of the spell, the spell is successfully cast.
If a spell is cast, the opposing player can choose any one of their wizards that is within 18" of the caster, and that can see them, and attempt to unbind the spell before its effects are applied. To unbind a spell, roll two dice. If the roll beats the roll used to cast the spell, then the spell’s effects are negated. Only one attempt can be made to unbind a spell.
That said, if it's unbound, then the effects are negated, so you wouldn't set up the models, and therefore you wouldn't pay the points, since:
General's Handbook 2017 wrote:“Each time a unit is added to an army during a battle, or a destroyed unit is returned to play, you must first subtract the number of points the unit would cost from your pool of reinforcement points, unless noted otherwise.”
Since you didn't add the unit, you don't pay the points.