Costs for non-slotted abilities are x1,5 in 3.5, not x2 like in 3.0.
12.000 gp for the Mage Armor (see the ring in Sword & Fist)
3.000 gp (2.000 x 1,5) for the +1 natural armor bonus
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15.000 gp total
4.000 gp for wisdom
6.000 gp (4000 gp x 1,5) for the dexterity
6.000 gp (4000 gp x 1,5)...