Principle:
The game intends to teach about magnetism, and momentum.  Children learn about magnetism by the interaction of the magnet on the pole and the ball, while trying to navigate the ball through the maze, they need to stay close enough to the ball while not getting to close as to get the ball stuck to the magnet.  The also learn about momentum while trying to avoid the holes, because they cannot just simply suddenly stop the ball to avoid a hole.

Interaction:
The children interact with the toy by using the magnet on the pole to navigate the metal ball through the maze.

Cost, durability, safety
Cost would probably be around 10 dollars to construct the maze out of wood, and also to have the metal ball and magnet on a pole.  It would be very durable because the maze would be made out of wood, but the string on the pole may need to be changed occasionally.  The toy is intended for older children because of the small ball, and also because younger children would probably get more frustrated with the game because their coordinatioin is not quite completely developed yet.