I have no idea about food prices in your part of the world, but being a high school student living on a very small budget (think $200/month for food expenses, and this is Denmark which is relatively expensive) I have learnt a few tricks. One of them is baking your own bread! I have an electric mixer with some special tools for dough, so I spend 15 minutes every two days and have pretty good and cheap bread. Soups are…
It's not the right season at the moment, but you could also consider growing your own stuff in the garden. Fresh herbs from the grocers are $$$, and don't taste/smell as good as what you pull and carry to your stove.
Commercial tomatoes breeds are optimized to have a tough skin, so that they can be thrown into large containers while green and hauled to the grocery store while ripening. None of this has anything to do with tasty or healthy. Growing your own tomatoes is also easy if you have a sunny spot, and you can pick varieties that taste better than what you'll end up with from the store.
None of these are cost-optimizing in a large way, but if you're going to be cooking anyway, you might as well enjoy better taste and the satisfaction of producing something physical and tangible.