Insert-able and under $100.00? I'd suggest Fun Factory's vibrators. Not the G4 line, since those go slightly over your budget (129.99 a pop!), but their classic and mini lines. I don't own any, but I know the silicone is good quality and reviews rave about the rumbly vibrations.
Personally I've been looking at getting one of the L'amour vibes for my first insert-able vibrator, the Passion G, Romance, or Desire. All three are under $50, silicone, and reviews say they have rumbly vibes.