"Custom" weapon enchantment for a two weapon fighter.

[thflame]

Would it be broken to allow the "dagger of doubling" effect on a custom upgrade-able weapon? I have a player that wants to dual wield wakizashi, but doesn't want to ultimately dump 400,670 gp in character wealth into two weapons, especially since she is also getting a splitting shuriken. My attempt at reverse engineering the dagger of doubling puts the cost of the "doubling" effect at +8000 gp.

MATH:

10,302 gp (dagger of doubling)
-2 gp (dagger)
-300 gp (masterwork)
-2000 gp (+1)
= 8000 gp

Does this sound reasonable, or should I price the effect as a +1 or +2 weapon ability?

Keep in mind that the player would like to have her weapon upgraded to potentially an effective +10 with the doubling property. As it stands, that would yield 2 identical effective +10 wakizashi at a cost of 208,335 gp.

[chaoseffect]

I think Doubling is a really bad thing to look at as a straight 8k upgrade, or even a +1 or +2 property. It is stupidly good for the WBL save if taken to its logical extremes. That said, I do agree that Two Weapon Fighters do get shafted WBL wise, as does anyone else who wants to have more than one weapon. I would consider not quantifying it (i.e. don't introduce this as an effect anyone can take in your world), and just make it a unique item for the player if you wanted it to be a thing at all. "This particular Wakizashi is unique because of story reasons" kinda deal.

Alternately, you could consider an Amulet of Mighty Fists as a base... maybe instead of unarmed/nat attacks it could be tied to a few specific weapons?