How much is the Plan: Staff of Herding worth?
Solution 1:
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.