Quote Originally Posted by arguskos View Post
By RAW, the costs for producing golems can't be mitigated by acquiring your materials personally. The rest of the cost is made up somewhere else.

Then again, should Mr. Archmagi's DM rule differently, I would approve heartily! I like players who take initiative on item creation.
I don't know for the shadow golem but the entry for Iron Golem gives us this :
An iron golem’s body is sculpted from 5,000 pounds of pure iron, smelted with rare tinctures and admixtures costing at least 10,000 gp. Assembling the body requires a DC 20 Craft (armorsmithing) check or a DC 20 Craft (weaponsmithing) check.
(...)
Cost 80,000 gp + 5,600 XP
We know that iron cost 1sp per pound. So, that's about 500 gp for the raw material. You can then reduce the cost of the Golem by 500 gp if you find a way to get free iron.

If Shadowiron's price is higher than normal iron, then the economy might be greater.

It sounds logical to me, at least... but I'm not the more rational mind around.