Lunch is $2.00 here but DD has never purchased it. I wouldn't want her to at all (I am very careful about nutrition and only buy organic dairy & produce), but I wouldn't stop her if she felt strongly about it. Middle school is tough enough as it is without being the "out" kid. Fortunately, she's very into nutrition as well, and thinks it's ridiculous what qualifies for a nutritionally balanced lunch.
Averaging out what I spend to pack her school lunch daily (I pack another mid-day meal for her to eat between school & when she skates each day), I'd say it's between $2-$3, but $1 of that is for the aseptic pack of organic milk she takes each day, which can be closer to $1.25 each if I can't pick them up at Trader Joe's). Then another $2-$3 for her after-school meal. I guess it does add up, but I would much rather cut corners if necessary elsewhere, rather in her nutrition. It really does make a difference. I can tell in her performance if she's has a "junk food" meal earlier, like fast food, so we avoid that out of necessity.