While we may often look for the most economical way to pay for big expenses, it is often the less obvious little purchases that end up putting the biggest dent in our wallet in the long run.
We buy many premade things out of habit that we could easily make ourselves and they cost us much more than necessary. For example, while the average loaf of bread may only be around $2-$4, that is actually near the average price of a bag of flour. For roughly the same amount of money you may spend for one loaf of "bread" (which may be so loaded with chemicals, preservatives, and fillers you may rethink the name given it), you could purchase a bag of flour and yeast to make your own bread and get more at a lower cost per unit. Of course, this may depend on other factors, like what you choose to put in it, if it was on sale etc...but in general it is safe to say it is cheaper to make your own. This goes for other things as well. But there are other benefits to making your own food. Not only does food tend to be less expensive when you make it yourself, it tends to be healthier.
By buying your own ingredients you can avoid many of the additives and preservatives often put in premade products to increase shelf life. You can also know how fresh your baked goods and other items are if you make those yourself instead of guessing how long that loaf of bread or whatever has being sitting in the store before you bought it. Another benefit is when you buy basic ingredients (such as flour, sugar, and so on) you can get more use out of them because you can make many things sweet or savory using basic ingredients. With premade food, for the most part, what you see is what you get, so not only is it less cost effective in terms of price, little variety can be gained from the purchase. So you should make your own food whenever you can, especially the basics you may use on a regular basis,, like bread, granola, etc.
If you want quick and convenient meals, it is best to plan ahead and pre-make your own. It does not have to be hard. When you do have time to cook simply double the recipe for something you enjoy and put some aside in the freezer for later, or prepare some dry ingredients for a recipe in a zip lock bag or some other container with the appropriate amount of liquid ingredients needed to complete it written on it so you have something on hand when you lack the time to cook from scratch. If you are planning on baking more than one dish, I suggest starting the dish that takes the longest to cook first followed by the things that take the least amount of time so the oven doesn't have to be on any longer than necessary to save electricity. Rather than purchasing things for convenience now you can save time and money by cooking in batches for your convenience ahead of time; just make sure it is no more than what you can use in a reasonable amount of time so it is not wasted by spoiling or freezer burn. Purchasing premade food can be an expensive habit in the long run, which is something you should avoid, even if you are not super broke.