Spell Cost

A spell's Magicka cost is determined by several different game settings and the spell's magnitude, duration, area, and whether or not its range is Target.

(BaseCost*fMagicDurMagBaseCostMult)
(Magnitude^fMagicCostScale)
Duration
(Area*fMagicAreaBaseCostMult)
(IsOnTarget*fMagicRangeTargetCostMult)

If any of the pieces of the formula are less than 1, 1 is used instead.

The game settings fMagicDurMagBaseCostMult, fMagicCostScale, fMagicAreaBaseCostMult, and fMagicRangeTargetCostMult have default values of 0.1, 1.28, 0.15, and 1.5 respectively.

The actual cost to cast these spells is further modified by the caster's skill in the appropriate school of magic (which itself is modified by the character's Luck):

fMagicCasterSkillCostBase+(fMagicCasterSkillCostMult*(1-((Skill+(0.4*(Luck-50)/100)))

The GMST fMagicCasterSkillCostBase defaults to 0.2 and fMagicCasterSkillCostMult defaults to 1.2.