Adamantine Weapon Costs

[Enguhl]

Excluding ammunition, why is there a flat cost (added) for adamantine weapons?
One would think a great sword and a dagger use different amounts so they add different costs. Has anyone made/seen a change to this where it adds cost based on weapon size?

[Jasdoif]

Were I to guess, it's because the benefits of adamantine weapons aren't dependent on the weapon's size, except for the item's hit points. An adamantine dagger ignores DR/adamantine and object hardness under 20 just as well as an adamantine greatsword does. I doubt a handful of hit points of difference is worth the trouble of having multiple weapon-price categories, and I imagine the designers didn't think it was.