Jessi of Rosy Revolver had a call on her blog looking for input on how designers price their work. Though I am not at all in her league, I felt that I could contribute what I have learned over the last 4 years. As said before by others it is an evolving process everyday.
Always remember that your time is worth it!! Then it is onto all of your material costs (even the little stuff), design time, cost of putting it in your shop if you are on Etsy, packaging, show costs,etc.
Let me turn you on to a few others that can do this better justice than me and that have already contributed to Jessi's post Bella-Bijou Jewellry and Nova of Sweden.