Having prepared sandwiches at industrial scales yo would be surprised how much you can scale down costs, bulk purchases can make a suprising difference. I really envy the system that most Japanese schools have in place. They seem to be focussed on the outcomes, not the cost or social engineering. I have talked with some Japanese friends about this and while a few are from wealthy families and attended schools without a formalised school lunch program the majority talk about how it opened their horizons as far as food options, gave them a sense of community, and was just a defining characteristic of their school life.