I would estimate that the largest part of a pizza joint's costs are no where near being related to food cost. In all honesty pizza is one of the cheaper foods to make since in bulk the ingredients are rather economical.
With all due respect, you are wrong.
Let's look at it this way: say your fixed costs (not including start-up equipment) such as rent, utilities, and payroll are $10,000/month.
Now if you plan to only sell 50 pizzas a day at $15 with a food cost of 20% (and let's say 30 operating days a month for the sake of round figures) gives you $22,500 in revenue and $4,500 in food cost (i.e. direct cost of sales). That's about 30% of your fixed/variable costs per month.
On the other hand, if you want to sell 150 pizzas a day at $15 with 20% food cost then your revenue is $67,500 and your food cost for the month is now $13,500. That's obviously well more than the $10,000 fixed costs and the ratio now goes up to 58% of your total costs of doing business (more or less).
You need to always look at both fixed and variable costs. Food cost is expressed as a percentage for this reason. Counting on food inventory items to be "economical" is not enough. One needs to be diligent with the numbers and understand the whole operation.