Great interactive graph by Planet Money explaining why there are 74,476 Reasons You Should Always Get The Bigger Pizza! This is good interactive look at how areas grow exponentially, but the prices of the pizza do not!
I have paired this with Robert Kaplinski's Which Pizza is a Better Deal? in my MYP 1 Math unit looking at starting a pizza business (interdisciplinary with Design Tech where they are working on baking the pizza). We will look at unit cost for their pizzas, and then create a business plan to determine how much they should charge to make a profit on their pizzas.
If you would like to do this with MYP 4-5 I would suggest using Dan Meyer's Pizza Doubler activity.