It doesn’t seem that cooking your own meals will save you a lot of money, if you live alone. There are stores that make and sell banchan, which means you don’t need to make banchan yourself.
What about rice? Stores sell instant rice for use with microwave ovens, except they are overpriced compared to using a rice cooker or if don’t want a rice cooker taking space, you can still cook rice in bulk with a pot without spending much time.
There are also small restaurants serving dosirak which you can take out. They serve rice and banchan.
No need for cooking at all then? One can still cook their snack food. Boiled eggs are especially easy to make and easy to store. You may find that eggs don’t fill you up, in which case, you may eat additionally carb or fiber. The carb, you can get from cooked rice, which is also easy to make and store. The fiber, you can buy pickled radish or kimchi. You can also think “I don’t seem to get enough greens when I eat out” and that means you are going to cook greens to balance things out.