Where are the rules for crafting Skill Enchantment bonus items?

I have been looking at guides for dramatically boosting a character’s potential with a single skill. In addition to toolkits, I have found mention of Competence bonuses and Enchantment bonuses (or “Enhancement” maybe?), but I cannot find the actual costs of making the skill enchantment bonus items. I have seen many references to these bonuses but am failing to find the information needed to craft them.