Sekura Group

To get the Nightmarish, Hellish or Infernal version of Plan: Staff of Herding you will need to go to the last part of Act IV (Prime Evil) on the difficulty you desire and then talk to Gorell the Quartermaster who is standing next to the healer, he will sell it to you for 1 gold.

Upgrading the staff at the blacksmith costs:

200,000 for Nightmarish Staff of Herding
500,000 for Hellish Staff of Herding
2,000,000 for Infernal Staff of Herding

1,000,000 for Infernal Staff of Herding

Taze (!empty($user->lang['WROTE'])) ? $user->lang['WROTE'] : ucwords(strtolower(str_replace('_', ' ', 'WROTE')))(!empty($user->lang['COLON'])) ? $user->lang['COLON'] : ucwords(strtolower(str_replace('_', ' ', 'COLON')))

1,000,000 for Infernal Staff of Herding

This is 2 Mil atm, unless they are changing it in patch