I'm making beef stew tonight for our family of four. All these prices are from memory during my last shopping trip.
2 lbs. of hormone free chuck roast @ $2.98/lb (-$2 off coupon) = $3.96
3 lbs. potatoes @ $.99/10 lbs = $0.30
1 lb carrots @ $.68/lb
1 med. onion @ $0.54/lb = ~$.40
1 lb bag of mixed frozen vegetables = $0.69
1 can low sodium beef stock @ $0.88
spices = ~$0.25
Total = $7.16
That will fill us all up for not a lot of cash, is better than fast/junk food, and there will be plenty left over. I could add some more potatoes and carrots for almost nothing and stretch it much farther. If I add a simple green salad to the meal it will up the price by maybe $2.50 at the most.
Avoiding junk food and eating cheap is more about smart shopping. When you do things like buy whole chickens on sale for $.79/lb, roast them, then cook the leftover bird down for stock or soup or chicken and dumplings, your food dollar goes a long way and you eat just fine. You might still get fat though.