I'm making a little dwemer robot that follows you around, and can "transmute" gold into Ingots of any kind. By this I mean that he is a vendor with 999 of each ingot, but I don't want the player to be able to sell to him. I've given him 0 Gold, but I'm concerned about players buying ingots "for free" buy just getting their gold back by selling him equipment. This goes against the flavor I'm trying to set up.

Maybe I can set the vendor chest to have an OnContainerChange event that basically says
if akItem != Gold001
akItem.remove()
endIf

??

Any ideas?

Hmm. My idea wouldn't work, it would just get rid of the item after the player had the gold. Darn.

Nvm, I just restricted his buy/sell list to VendorItemOreIngot

Just took a look at the http://www.creationkit.com/Creating_a_Merchant tutorial and you can use formlists to set what a merchant sells and buys... Unfortunately, this still won't work for you if the player has the merchant perk to sell any item to any merchant.

Could you just create a dialogue option for each type of ingot and then remove the gold from the player?

You wouldn't need to have a chest at all. Simply have him remove the gold and the "From" ingot type from the players' inventory, and drop one of the "To" ingot type.