
Captain Sir Hexen Ineptus |

First: Mithral costs 500 gold per pound of the original object. Yes it is x8 weight for this size. Gargantuan full plate weighs 400lbs costing 200000 gold market cos, so it 66667 gold rounded up. Mithral is not magical so it is a trade good.
Trade goods are the exception to the half-price rule. A trade good, in this sense, is a valuable good that can be easily exchanged almost as if it were cash itself.
Now note this.
An item made from mithral weighs half as much as the same item made from other metals. In the case of weapons, this lighter weight does not change a weapon's size category or the ease with which it can be wielded (whether it is light, one-handed, or two-handed). Items not primarily of metal are not meaningfully affected by being partially made of mithral. (A longsword can be a mithral weapon, while a quarterstaff cannot.) Mithral weapons count as silver for the purpose of overcoming damage reduction.
Weapons or armors fashioned from mithral are always masterwork items as well; the masterwork cost is included in the prices given below.
Mithral has 30 hit points per inch of thickness and hardness 15.
Type of Mithral Item Item Cost Modifier
Light armor +1,000 gp
Medium armor +4,000 gp
Heavy armor +9,000 gp
Shield +1,000 gp
Other items +500 gp/lb.
taking into effect the x8 rule for the armor and the non magical cost to create being 1/3rd it would cost you 28000 gold.
So by this logic you magically create 38667 gold (66667-28000) by making the armor and milting it down for raw mithral.

Kierato |

Mithral full plate is 10,500 gp, and gargantuan is X8 making it 84,000 gp, not 200,000 gp. It's armor, not other items. Also I disagree with the trade goods part as mithral is very rare, much rarer than platinum. Furthermore, that 500 gp/lb for other items is a finished value, not a value for 1 lb of mithral.