This is my formula: materials+labor+ misc=base cost X at least 2-5. Ok, so materials is obvious, your labor, give yourself an hourly wage and then pay yourself for the time it took. Misc, for me is $2.00 which covers packaging and bus cards. You have to at least make all of this back on the piece, your profit needs to at least double this or it won't be worth it. If you ever plan to sell wholesale, or want room to give someone a deal, you need to mark higher then x2.
I usually mark my earrings x5 and my necklaces and bracelets between 2.5-4. I work out an estimate price and then round it up or down depending on what I think my local clientel will pay. My necklaces go from $35 - $70, my earrings $12-$30 and my bracelets $20-35. I use semi-precious stones and sterling/fine silver and do mostly wire wrapping and some silversmithing
hth