Cook a big pot of beans from dry beans once a week--use that for refried beans in burritos/tacos one night and then add ground beef or leftover chicken and lots of veggie filler (onions, peppers, kale) to make bean soup or chile for another dinner. Offer brown rice or a whole baked potato with every meal--nutritious and filling! Eat seasonal produce, get a CSA if you can afford the upfront cost--for your price per pound, you will get a lot more than at the grocery store (at least that's been my experience). See if you can buy in bulk with a friend and split the cost for mainstay items like flour and meat. Every time you go to the grocery store, get a pound or two of dry beans and use them to make hummus/bean dip, etc for sammiches, wraps, and dips. Eat a lot of carrots with those dips--carrots are cheap!
Eat a big green salad every day--my grocery stores usually have at least one green leafy variety pretty cheap--let that salad be a main course for lunch a couple times and for dinner another time--like asian chicken salad or taco salad with black beans and yogurt for sour cream. When you see things that store well (like butter which can be frozen) on sale, stock up--you will be glad you did! Use yogurt as a staple for condiments (sour cream, dips, soup toppings, smoothies, etc.) and buy the big tub. Oh, you can freeze cheese, too--we buy two of these big tubs of feta when on sale, freeze one, eat one. Same with those really big Tillamook cheeses, cut it in half and freeze half--the hard cheeses get a crumbly texture but I can live with that or use it in a recipe where it's just going to be melty anyways.
Source local eggs--we can get them much cheaper from local yard chickens than from the store. Oh, that makes me think of breakfast--I buy a big bulk bag of steel cut oats and another of brown rice grits and alternate those with eggs for breakfast. And about meat--instead of it being the center of the plate, wrack your brain for your old vegetarian mainstays, and then use the meat on the periphery to save money--like quesadillas with a little ground beef or chicken instead of a whole chicken breast by itself, kwim? Or stir-fried rice with lots of vegetables and a little diced pork or whatever you prefer.
See if there are local farms around where you can you-pick tomatoes or fruit--usually much cheaper than grocery store prices for those. Make a big batch of no-knead bread (we use the 5 minute artisan bread recipe) and use that dough for pizza/focaccia one night, pita (goes good with cheap dal!) another night, and the rest for a loaf of sammich bread for lunches (using those bean spreads, of course!). Can you find turkey on sale? You could roast a big turkey and then freeze the portions for sammiches, gravy, soup, etc. My big tool is buying in bulk and using what I can, freezing, canning, or dehydrating the rest--it's worth the extra work!
I hope any of that helps ;) I just was thinking off the top of my head things that we do here or that I am trying to do more of.
With all that said, we have a former veg thread going on the main Nutrition and Good Eating page here: http://www.mothering.com/community/forum/thread/1298565/questioning-or-former-veg-n-support-chat that you might be interested in