It doesn't require the Merchant skill.
Per the ARB, pg 149,
Production Points and/or Coins: For each Goblin Point turned in, you can receive one Production Point which can then be used to “purchase” coins, scrolls, potions, elixirs, gasses, traps, weapons, or armor. During checkin, state what you wish to use the Goblin Points for and Logistics will provide the item(s). You cannot spend more than one hundred Goblin Points per regular event (two gamedays). For modules (25% Experience) you can spend twenty-five; for long weekends (worth 150%), that’s one hundred and fifty.
Spell ink doesn't have production points, so the cost of adding spells to your spell book is based on your local chapter. Currently, the cost in Alliance Seattle is 2 copper per spell level.