For under $100, you can't get any better than a Wacom Graphire3.
However, I'd personally recommend saving up a few extra bucks to get the larger, 6x8 Graphire3 Wacom makes. The extra space allows you to be more natural with your hand movements while drawing.
Also, when you do purchase your tablet, keep a this in mind:
- Your first work with the tablet will probably leave you frustrated. For most people, it takes a while to get used to drawing on such a smooth, textureless surface. It's also a hard transition to force yourself to stare at the screen and NOT your pencil. It'll take time.