Check out the shoestring meals sub-forum (in the Food area)
http://www.3fatchicks.com/forum/shoestring-meals-235/
There are tons of threads with shopping tips, money-saving ideas, menus, recipes.... loads and loads of information.
Hubby and I went through a rough patch where our monthly food budget was as little as $25 for the month for both of us. When it was that low, we did eat a lot of pasta and rice, so it was higher carb than it should be (hubby and I both have blood sugar/diabetes issues), but we ate relatively healthy by focusing on the cheapest veggies (OMG, did we eat a lot of cabbage. We ate cabbage with everything but breakfast - take that back - sometimes we'd have soup for breakfast). We bought the cheapest fruit we could find, which usually meant bananas (Kwik Trip a local convenience store sells bananas at 38 cents a pound and apples, oranges and pears for 3 for $1).
I've always used exchange plans when dieting (and in general they're also good plans for non-dieters because they're based on a balanced diet - though you can "tweak" them to fit your own idea of balance. For example, I eat a relatively low-carb plan so I found a low-carb plan and adjusted it to my own ideas of balance. It differs from a "standard" plan by having more protein exchanges and fewer bread and fruit exchanges). My hubby didn't follow an exchange plan, but I still used one for him when shopping.
What I mean is that I used an exchange plan to grocery shop. My food plan requires 3 to 4 fruit exchanges per day. I know that bananas count as two fruit exchanges. Hubby usually only eats 1 - 2 servings of fruit per day. I usually eat my full 4 servings. That means I need to buy 28 pieces of fruit for me and 7 to 10 pieces for hubby. For most fruits, that means 28 small pieces of fruit or 14 large pieces.
If the budget is very tight, I might buy all my exchanges from bananas. Bananas ripen (and spoil) quickly on the counter, but as soon as they get to my ripeness preference, I put them in the fridge, which slows the ripening and extends the shelf-life (but the skin gets black, but the inside doesn't get mushy at least not within the week I keep them).
I do that for all the "exchange" groups. I know how many exchanges of each type I need for the week, and I can estimate fairly well what my husband will eat. So I look through the grocery store flyers and make a list based on which foods are the cheapest. I buy the cheapest I can find in each exchange category.
We do also buy in bulk when we can (thanks to a chest freezer we were able to purchase one year with family Christmas gift money). We eat TONS of dark meat chicken, pork, and ground beef because those meats go on sale frequently. We take advantage of sales when we can. Just as an example, corned beef was on sale after St. Patrick's Day. The price was great, but since corned beef sometimes isn't very good, we only bought one large roast. Hubby made it the other day in the crockpot, and it was so good we wished we had picked up more. But corned beef, even a good one isn't the healthiest meat, because of the salt and sometimes nitrates.
We "extend" ground beef with tvp, textured vegetable (soy) protein, also called tsp. We can find it at Walmart for about $5 per pound, but in Bloomington, IL it sells in health food stores for under $3 per pound and under $2.50 per pound if you buy it in a 20 lb bag. When we visit my family there, we buy several pounds and when they visit us, the bring us several pounds. We have never bought it in the 20 lb bag (though I've been tempted).
We buy the variety that looks like GrapeNuts cereal (or beige aquarium gravel). Hubby doesn't like it plain (you add hot water to reconstitute it). I don't mind it. However hubby does like it in ground beef, so I brown it with ground beef and seasoning veggies (onions, celery...) and then freeze it in large ziploc bags. This way, I can turn very cheap, fatty ground beef into a low-fat ground beef mixture. As it freezes, every 20 minutes or so, I shake, moosh the bag so the tvp/beef mixture freezes in "crumbles" that I can scoop out as needed to make chili, sloppy joes, soups, spaghetti sauce, omelette filling, hamburger-helper style rice and pasta skillet casseroles...
I found super cheap "ground beef recipe" cookbooks on amazon and at garage sales (even with shipping I paid less than $5 per book), and I use the tvp/beef mixture anywhere a recipe calls for browned ground beef.
A book that really helped me tremendously was "The Complete Tightwad Gazette" which I also either bought at a thrift shop, garage sale, or amazon.com used for less than $5 (because $5 is the absolute limit I will pay for a used book in most cases).
I also bought the book "Dumpster Diving" for my dad as a Father's Day gift (I spent less than $10 for it too and had it sent directly to him). It was a bit of a gag gift because my dad is known for bringing "curb treasures" home and fixing them up and then giving them as gifts. The next time we visited, I read it while we were there (I'm a fast reader). I don't really dumpster dive myself, but the book was very interesting and fun to read.
However, it got me onto the hobby of saving money, and I borrowed just about every book the library had on frugal living and saving money, and now we NEVER buy anything (except socks, underwear, and shoes) new that we can find used, and we can find used most of the time, and often used is better. We can't afford "good" furniture, but good furniture is sold very cheaply (and even often given away) in thrift stores and at garage sales and on freecycle (check yahoo and probably facebook for freecycle groups in your area).
Freecycle is awesome. People post when they have stuff to give away and you can also post what you're looking for. You'll even see furniture and computers being given away (and once we even saw a mobile home given away). In the summer, people list extra garden produce they have to give away (we live in a relatively small community, so this is safer than it would be in some).
Craig's list also has similar postings.
I'd highly recommend the Tightwad Gazette and similar books though. A lot of the tips are extreme enough that you'll think "absolutely no way, would I do that," but you ignore the crazier stuff and just use the tips that work for you.
It was from the Tightwad Gazette that I found the idea to mix ground beef and tvp, though I tweaked the recipe. I also make several versions. For example, I love the flavor of Chorizo (and Aldi and a local mexican market both sell very inexpensive chorizo - the mexican market being a tad more expensive but a lot higher quality), but cheap Chorizo tends to be extremely fatty. Problem solved though by browing the Chorizo with tvp (which has virtually no fat at all). And since the flavor of chorizo is so strong, you can use more tvp than chorizo. I brown the chorizo with the dry tvp, and let the tvp soak up the meat juices and fat (I'm going to use so much tvp that I don't really have to drain the fat unless I want to - I usually don't). Then when the meat is nearly cooked through, I'll add the water you need equal parts liquid (water or broth usually) to reconstitute the tvp. So if you use a cup of tvp (equivalent to about a pound of ground beef) you have to use bout a cup of liquid to reconstitute the tvp. With some chorizo, I can add 2 cups of tvp to one pound of sausage (making the equivalent of three pounds of chorizo for only about $4).
We'll make tacos or stir it into rice and beans.
We shop Aldi, Walmart, (and now Target) a lot. We've slowly learned which stores are cheapest for which foods. We stop at Kwik Trip for bananas, fruit, butter, and milk - because they're the cheapest in town for that.
When we can only shop one store, it's usually Aldi or Walmart, but usually we shop several places including an Asian grocery (because bulk rice and rice noodles are cheapest there and we can buy gourmet soy sauce by the quart for the price of the cheapest soy sauce in the grocery store). I like asian veggies and herbs like eggplant, cilantro, green onion, cabbages, and green onion -in our area these all tend to be cheaper and/or better quality in the asian groceries than in the standard grocery stores.
We also shop dollar stores and salvage grocery stores (sort of like Big Lots - they buy out and resell other stores' bankruptcy and overstock). The salvage stores sell only shelf-stable stuff, and while there are some good bargains to be found, there's also a lot of cheap junk food. However, we buy cereal and oatmeal dirt cheap and find all sorts of surprises. Last week, we found a large gallon of peanut oil for only $2, which will last us a very long time.
This is also a tip I learned from The Tightwad Gazette.
There are also great online websites (just type frugal living, living on a budget, eating cheap, saving on groceries and other similar phrases into google and you'll find tons of them).
One thing I don't usually do is use coupons, because I rarely find a coupon for a product we use (since most coupons are on prepackaged junk foods), however when I do find coupons I want to use, I go to our closest grocery on Wednesday or Saturday because the store does double coupons on those days. When I do have a coupon, it often pays to buy the smallest box, but I compare the prices to be sure (I always take a calculator and a small notepad to the grocery store).
I know I've practically written a book, but there's tons more info from other 3FC members on the Shoestring Meals forum. Eating healthy cheaply does require more work and time, but it gets easier and easier as you do it (and a crockpot helps a lot. You can often find crockpots - often still in the original box, never used, at thrift stores like Goodwill).