A lot of people (in the USA at least) think that you need to eat a lot of protein, or that protein in and of itself builds muscle. This isn't exactly correct since the average American eats something like 1.7 to 3.5 times the 'recommended' levels [1] of protein (which may already be too high of recommendations). It's appropriate to note that America is known for its high levels of obesity and diet-related illnesses.
While it's true that you should get a sufficient amount of protein, studies have shown that eating extra amounts of protein does not produce an increase in muscle gain when body building. In fact, it's known that eating excessive amounts of protein can have harmful effects. [2]
If you want to build a little bit of muscle, focus on healthy foods. Your body will burn off excess fat which helps show off muscles, plus you'll be getting the nutrients needed for healthy weight gain (i.e. lean muscle mass). From there, even small amounts of muscle-building exercise goes a long way. I suggest basic push-ups and sit-ups for core muscle building, find some weights for biceps/triceps.
I spend next to nothing on food, but everyone in my smash scene knows my brother and I by the awesome/healthy food we eat.
First of all, ditch the soda! Not only is it a waste of money, it literally is poison. Seriously. People build up habits of drinking soda thinking they like it, but if you stay away from it for at least a month you'll be able to taste it for real and it doesn't even taste that good. It definitely won't taste good enough to warrant the harm it causes your body.
Some of the cheapest foods are some of the most important foods you should be eating. Beans and grains are pretty cheap, but that makes up about 70% to 90% of your caloric intake right there! You can also create a huge variety of foods from cultures all around the globe with just beans and grains.
It's the pre-packaged, nutrient-shallow foods that should be avoided. Eat whole grains with legumes and an appropriate side dish.
Boxed cereals are over-priced and nutritionally shallow. This goes for brand-name boxes cereals as well as generic. They're all fakes and crooks.
Again, whole grains are great for meals, especially breakfast. Try rolled oats - they cook quickly and provide a lot more energy than fluffy boxed cereal. Oats are also very cheap, make a lot, and with the money saved you can buy things like almonds, raisins, walnuts, cinnamon, apples, agave nectar, bananas, or whatever you want to add to your "Real Cereal".
Find something that isn't pre-packaged for a snack. I'm pretty much talking fruits (but even vegetables make for great snacks). I'm talking about apples, bananas, pears, oranges, avacado, carrots, celer... whatever is in season. Peanuts, cashews, almonds, dried fruits also make good snacks. I even bought some asparagus for a snack one day.
These 'snacks' are packed full of vitamins and minerals, but most importantly you're not putting artificial or synthetic ingredients into your body (most pre-packaged snacks have several such ingredients). And hey, looks like you don't need to buy multi-vitamins anymore! Spend that vitamin money on yummy whole foods.
tl;dr
Your health is one of the most important things in your life.
If you don't have your health, you don't have anything.
