You need 4000 gold and caster level six. Also, keep in mind that you can only have, at most, three enchantments on your weapons. Mithral and adamantine materials take up an enchantment slot as well.
Taken from Thieves-Guild:
To add an enchantment to an item, select the Enchantment recipe books in your inventory, and open it. Select the recipe you wish to use and right click to open it. Examine the recipe to make sure you have the appropriate ingredients. Note the enchantment recipes for weapons and armor do NOT require spells. If all of the requirements are met, simply LEFT CLICK on the appropriate enchantment. Then target the item in your inventory that you wish to enchant, apply the enchantment and presto, the item gains the property.
In addition to the appropriate ingredients, there is also a gp cost associated with enchanting items which can range from 500 to 9000 gp. This process requires the Create Magical Arms and Armor feat. Recipes for enchantments will also have Caster level requirements.
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