The cheapest way to get to Mousehole is to walk, and there are good views, pubs, and a few small shops along the way, but once you've done that you can also take the First Bus from one of the stops in Penzance, Newlyn, or Marazion. The bus drops off and picks up right in the center of Mousehole. It's cheap (I think it costs just over a pound) and comfortable. Visit the website below to plan your trip or see the times.