Next, split the class into teams, give them an imaginary target budget with all the elements they need to make a film (actors, script, cameras, effects, publicity) written on cards bearing a price tag. Then start the game.
Teams have to decide how much to spend and what eleents they want to use within a set time (20-25 minutes). They can choose as many cards as they wish. They must also list the costings to show the executive producer (you). They can take longer than the time specified, but for every extra minute they forfeit some of their budget in lost studio time. For the plenary, ask the children to tot up their budgets and work out who has to pay a penalty.
You could prepare several sets of cards for differentiation and can also make the game more challenging by ensuring no combination of cards will amount to the target budget.