Twenty's generous enough already. The deal is an investment of trust, the streetear knows that the next rumour she picks up will be bought (assuming she's any good at gathering information). It's simple trade.
Except we're trying to get
her to trust
us: oni, by their nature, are honest to a fault, while we, a, well, Nue, are pretty much the definition of connivery. If we're going to build a relationship of trust, then we need to offer something to her, not demand that she give us something. In fact, her counter offer of us letting her know of juicy gossip would have been perfect to go with the offer of 20.
I'm with Fightest on this one. Besides, we're haggling. We're supposed to go back and forth until we reach an agreeable price.
When you haggle, you also need to offer something of value to them.
> How much do we sell a shot of something good for?
> If it's five or less, then: "Okay, twenty, I'll pass on something interesting to you,
and a shot of (insert drink here) to go with it."
The reasoning for the shot is that it's something an oni would be interested in, and it'll still be cheaper than twenty-five.