The toy above is made to demonstrate lift and basic physics. The child would use this toy by having a plane and two fans that are part of the package. Along with the plane comes "weights" that can be added. (This plane would be made of some light foam that can float but will not get blown around.) The plane would be in between the two fans and the goal would be to get it to stay afloat between the two by varying the weights and then placing it in the air flow. 

The cost would not be too expensive. The planes and fans would be small enough to manufacture relatively cheaply. It would be somewhat durable, however styrofoam can break somewhat easily, especially in the hands of children. Luckily, the fans would be the more expensive part of it all, yet they would be more durable. It would be made safe for children, as the rotors on the fan could be made of a styrofoam as well, similar to the hand held fans that you give little kids at fairs and such.