Here's the catch: If you're a group member, you get it for free!
Auryn Beorn has started writing a tutorial series that you can check for free at her personal blog: a guide for merchants. Link for the introduction and the first post:
- Merchant Resource: A guide for new (and not so new) merchants in SL
- How do I begin? Location, and information we want to always have handy, and preparing our inventory
She'll be adding more content in the following weeks. You can check for all the links on this page: Merchant Resource