Sanctum Prelate

• WWizards of the Coast2016-08-23
  Official Ruling
  For spells with in their mana costs, use the value chosen for X to determine if the spell's mana value is the chosen number. For example, if the chosen number is 4, a noncreature spell with mana cost couldn't be cast with X equal to 2, but it could be cast with X equal to any other number.
• WWizards of the Coast2016-08-23
  Official Ruling
  Effects that increase or reduce the cost to cast a spell don't affect that spell's mana value.

Rulings via Scryfall