I am going to go with idea one but have changed it a little. I have decided to use the metaphor of a coat check system. I have done this as it will make the exhibition more interactive. I will make a 'mini' scene of a coat check setup that people can interact with to help them understand how arrays work.
It will have little cost as I will use card and wire to make the scene. This may take a few of days to fully complete and an extra day for they 300 words.