How much should you charge for your work?

Props.com: "If you are a prop artisan, and you find yourself freelancing (or wishing to freelance), you may wonder how to make money, or more appropriately, how much to charge for your work. In my experience, it has been most helpful to calculate the costs of the project as accurately as possible beforehand, including a set rate you charge for your own labor. My favorite tool for this is the computer spreadsheet, whether it’s through Microsoft Office, OpenOffice, or Google Docs (or whatever Macs use).