I just got the Plan: Staff of Herding and was wondering what the drop rate was because a friend of mine wants to buy it. I know you can't put it on the auction house, so it's hard to estimate the price. Anyone else know how much it is worth?
The items for the Staff of Herding, including the Plan: Staff of Herding are "Account Bound" meaning they are only available to your Battle.Net account. If you want to give it to your buddy the only way is giving him your account password, and you shouldn't do that. You could say it's worth about as much as your battle.net account is worth :)
About your title questions: I killed Izual about 5 times before it dropped. Of course this is definitely not a scientific answer.