Like Veela, planning and cooking ahead of time has been a real budget and time saver for me. A huge pot of soup with homemade stock (made from bones or veggie scraps that I would have otherwise thrown away) can give me lunch for two weeks if I portion and freeze it. I do that with so many dishes so I'm not losing time or money with leftovers I don't eat. Plus they're portioned out for me and since they're frozen, I'm not tied to eating the same thing all week.
Beans and eggs are great, cheap sources of protein. Fruit like oranges or apples are little self contained snacks and are pretty inexpensive. Cabbage and cauliflower are my favorite cheap veggies and can be eaten raw or cooked, or mixed with rice, pasta, or potatoes (all inexpensive too!) to bulk up a serving and provide more nutrition.
One jar of tahini ($6 ish around here) will provide you with many, many batches of homemade hummus for so much cheaper than you can buy it premade. Similarly, salad dressing, yogurt, seasoning packets, and bread products are cheaper to make at home. We often pay for convenience - laughing cow cheese is so much more expensive than store brand neufchatel cheese (1/3 less fat cream cheese), but we use it because it's portioned/flavored for us. 100 cal packs seem so easy to grab and go, but if we get nuts in bulk, we can portion them out in baggies ourselves and save quite a bit!
It takes some time to figure out balancing food, time and what is worth to make at home, but it's entirely possible to make cheap, healthy, delicious foods. If you check
budget bytes or
eating richly, you'll see a lot of ideas that you may be able to implement.