Wow, lots of posts. I like ideas on 1st page. I did not read most of this thread, but I have ideas.

Below should be used as a guide,

Have item base cost based on rarity:  minor, moderate, rare, legendary, relic and Artifact.

Add additional cost based how many powers it has and/or what lvl spell the power mimics

Have a guide for monster parts based on HD of the monster to determine the gold value, which would go towards the creation cost of the item

Time should be based on rarity+ amount of powers. For example, 5 days per rarity+ 5 days per power