You get 2 swords for 20 gp. Check!
Masterwork both swords costs 320 gp. Check!
Magical enchantments or properties, each sword is individually priced. Got it!
What about special material? Specifically adamantine, but all in general.
That's my dilemma. The weapon is part of a concept character I am currently playing. I want to make them adamantine, but the description in Ult Equip is unclear about special material.
Weapons have +3,000 added to their cost to make them Adamantine.
P/inch 40 (weapons and armor normally made of steel that are made of adamantine have one-third more hit points than normal.; Hardness 20; Cost Adamantine is so costly that weapons and armor made from it are always of masterwork quality; the masterwork cost is included in the prices given.
So to make your swords Adamantine, they'd cost 6040gp for the pair, and the masterwork cost is figured into the cost of making the weapon out of adamantine.
Butterfly Sword are 20gp for the pair. So if it individually priced for special materials it would be 6020, but as it only cost 320gp for masterwork for the pair, it makes me wonder.
Hmm...
The safe answer is 6020gp
The other option I can think of might be 5720gp, as the masterwork for both costs the same, a price included in the making of Adamantine. These are still two weapons.
As the sword text makes exceptions to the costs of the masterwork, but not special materials we can assume that the price will not be 3020gp.
It is after all special materials :P