Why not just make healthy food cheaper?
Let's be honest, if we're talking supermarkets here, they can afford to both pay a fair price for the product they sell, and also price it reasonably for their customers.
Local grocers and butchers sell things cheaper already, so that shouldn't be an issue.
We should also revise our VAT system.
Frozen ready meals are VAT-free for example, but juice is taxed at 20%.
We charge VAT on products which HMRC doesn't feel are food items in their own right, but are actually things which would allow people to make their own healthier food - essential oils, bicarbonate of soda, etc.
Marshmallow teacakes are VAT-free but cereal is taxed at 20%.
Shortbread covered in chocolate is taxable at 20%, but if you add caramel to it it becomes VAT-free.
The only places near me to get cheap fruit and veg are Lidl stores, but these just aren't as abundant as stores like Tesco who have absurd monopolies.