If you are going through the worksheet to determine whether you are self-supporting, stop. You already said that your parents pay the majority of your expenses. Why torture yourself? If you are under 23 and a full-time student for at least one semester, then file as a dependent.
If you need this for filling out a scholarship form, think about how often you go out with friends and what it costs per month. Do you have a hobby, like collecting stamps, that you spend money on? A serious relationship with iTunes or Amazon? Don't sweat this. Make a reasonable estimate and move on.
