Maybe we can go a little higher, but Sora's right. I'm a witch, after all. This would really just be a little boost. How about [New, slightly higher price, because that's how haggling works. She knows this, she's seen it in movies.]

"A little boost? You just saw what it can do for yourself! Maybe you are trying to rob me after all... but I'll be generous, and offer it for-" [Another offer. Closer to the one Kairi made. She pauses a moment, and decides it's time to seal this deal.]

I think I know exactly what I can use this for, and what I can't. And I'm pretty sure any other witch is going to figure it out pretty quickly when they see it too. The powers, and the limitations. So I don't think you'll get more than... [One more offer.] That's my final offer. Take it or leave it.

[That's what people always say at the end of these sort of negotiations, right? Kairi sticks out her hand to shake with the Naga, who hems and haws for a bit... But finally grabs her hand and shakes it.

"Done. A fine bargain. You two impress me." [She holds out her other hand, still keeping a grip on Kairi's.] "So... payment now, since we had such a spirited debate over it."