hi! just read your post, there is a rule of thumb on pricing but it sort of leaves out the "art" factor. However, if you want to have a pricing base, here is a suggestion:
say you spent $20 on ingredients of your product, you can sell it for $60. we call it the rule of thirds where the price is divided into three equal parts: 1/3 ingredients, 1/3 labor (in this case if you are working at home, it is also treated as your income) and 1/3 overhead (should cover a portion of your utility bills etc).