Spell cost

[doofus]

How do I find out the cost in mana/energy/whatever of a spell? Outside of their base cost, some buffs or conditions change the cost of a spell. I typically use "IsUsableSpell("my spell");" but in this case I want to know whether I will be able to cast two different spells so I need to know their cost and then compare it to available mana. Is there an API function that might tell me?