Answer:
Oh my goodness! With the cost of supplies changing daily, using a formula like this (cost x 2) means that you are making your work for free! Please check out this article,
How to Price Your Jewelry, and begin making some money for your art!
You should also consider checking out The Definitive Guide to Selling Handcrafted Jewelry, which goes even further in-depth about pricing, selling, and other aspects of the jewelry business.
Answer contributed by Dale "Cougar" Armstrong