Thanks for the sympathy! Actually, it's not too bad - there will be other food, so
9 pizzas 12"x 16" should do it. I'm going to part bake the bases, then put toppings on and bake them off as needed at the party venue, using their ovens, and I don't have to see the kids.
As a matter of interest, a Margherita pizza that size costs me under £2, using best quality materials. stoneground flour from Bacheldre watermill, Berio olive oil, Napolina tomatoes and Costco's best mozzarella.