when I was running youth groups we used to buy the cheap $2 frozen pizzas and use them as pizza bases, then add our own sauce and toppings over the top of the original pizza. At the time, premade bases cost more than the frozen pizzas, and the minor amount of sauce and toppings underneath our additions added an interesting texture.
common recipe was frozen supreme pizza, with BBQ sauce added, assorted meats, capsicum, then cheese... also tried bechamel sauce (with cheese added), topped with roasted chicken (rotissirie from the deli), bacon, and a fine amount of thin sliced white onion.... a BBQ meatlovers frozen as the base worked best with that combination.
Never had complaints except for the one kid who insisted that 6 cups of topping on a 12" base was sensible, then wondered why the middle of his toppings were cold - every single time...