How to make lesser powers use mana?

[FWB]

Pretty much what the title says, i'm trying to figure out a way to make lesser powers have a mana cost attached to them. As of right now, even though it shows a spell cost in the spell properties, they require no mana. Barring the possibility of this, does anyone know how to make spells that can be cast by your voice. All I know is that if you try and make a spell that uses voice to cast with in the spell properties, you can't select that spell from the menu in-game. Any help would be greatly appreciated.