Fresh fruit and veggies aren't that bad if they're in season & purchased locally. Yesterday at the grocery store, I noticed apples were 69 cents per pound. All over the place, there are vegetable stands with a variety of squashes, usually 2 or 3 for a dollar. Fresh picked corn on the cob is generally $2 per dozen this time of the year.
Potatoes go a long way, ditto rice. Although, perhaps it's just me, but rice is rice. Potatoes are baked potatoes, french fries, home made french fries for those late night snacks, potatoes au gratin, etc. Boneless skinless chicken breast is generally pretty cheap (at least around here), ground beef isn't too expensive. Forget about steaks on that kind of a budget. Good steaks are expensive, cheap steaks aren't worth it.
Baked goods - why not go for the day old rack at the store that's discounted at least 50%? Sometimes that even leads to less laziness in cooking and BETTER meals. Instead of tossing that burger on a hamburger bun, you might be more tempted to rub some butter on top of the bun, sprinkle some salt on it, and toss it in the oven to toast it for a minute or so. Assuming you eat a burger on such a bun.... you're welcome.
I'm not much of a fan of the "meat every third day" thing. A lot of meals will stretch meat pretty far. Take a whole zucchini (3 for a dollar at a roadside stand), slice it down the middle the long way. Scoop out all the seeds. To make a filling for it, cook 1 lb of sausage (about $2.50), with part of a jar of spaghetti sauce (.99 for whichever brand is on sale this week). After cooking it down a bit, fill the cavity in the zucchini with it. Bake. After it's cooked most of the way through & the zucchini is really soft, put a layer of thin sliced cheese over the top & bake long enough for the cheese to melt & maybe even turn a little brown.
Don't get shredded cheese; that stuff works out to about $7-8 per pound. Get the 8oz blocks of cheese. Around here, one brand or another is regularly on sale for $2 or even 3 for $5.
That's a very inexpensive, hearty meal. Actually, probably two meals. Tastes even better warmed up the next day. Plus you'll have enough spaghetti sauce left over in the jar to have a spaghetti dinner. (Another incredibly cheap meal.) Bread from that day old or about to expire rack time: melt some butter (or cheap margarine) & add garlic to it. Spoon it onto the slices of bread & spread it out. Toss in the oven til crispy. Awesome garlic bread to have with the spaghetti dinner.
Another big tip to save a lot of money: plan on each meal actually being two meals. i.e. stuffed zucchini for dinner, left overs the next day for lunch. Big spaghetti dinner, leftover spaghetti dinner for lunch the next day.