Most Helpful Girl
Umm you should probably use Manic Panic or Directions. I've been told they are the best semi permanent hair dyes. I used them when I was in High School.
As for the bleaching, hmm what kind of purple shade are you aiming for? Can you link me a picture? I also want a picture of how your hair looks right now in order to help you more. I don't think you need to bleach it by the way. If your hair is a combination of dark pink to dark purple, there is no need to bleach it. Just wait till it fades out a slightly bit more.