Potatoes, apples, beans, and tofu actually are cheaper,
For one person maybe. Buying in bulk to afford to feed a FAMILY, no. The beans are cheaper, but enough fruits and vegetables to make a well balanced diet is not. And good luck getting kids to eat beans all day.
Even if your arguments made any sense, they would amount to saying that because low income workers can only spend 5 minutes on food preparation and afford only foods that make them fat, we should then spend thousands of dollars per year in medical treatments to alleviate the problems resulting from their obesity. Your premises are wrong, but even if they were right, your conclusion would still be ludicrous.
If a device that fixes the problem is cheaper than the problems, it is worth it.