Another way to look at it is this. Try to understand what you think you are going sale in your mix - i.e. 10 of product a, 15 of product b, 5 of product c, and so on.
Then, take all of your costs - both directly related to your product and your overheads (selling, general, rent, marketing, etc) and your profit requirement. Once you have all your costs - then, you can divide your costs out based on your sales estimates.
The problem with all of these methods is that you will not know how much you can sell until you get out there and start selling them.
So, you might just do this. If your item is $2.50 - market it up 100% - to $5. Do this with all products (within reason - if a product is $100 - you might want to try to sell it for $200). Then, as you move forward and see what sells - then you can adjust your prices until you research our goal. Plus, it is always better to start higher on price and come down then doing it the other way.