I’ve been vegetarian off an on for a long time but even when I am not trying to stick to a vegetarian diet I tend to eat very little meat for one reason; it’s cheaper.
You can get large ‘bulk’ bags of rice at most asian groceries (cheapest I’ve found is 20lbs for $15 but this is plain white rice, not jasmine). I prefer to buy large bags of brown rice as the whole grain completes the protein in beans.
Beans are also exceptionally cheap. Dry is cheaper at the outset but the energy used to cook them probably makes them more expensive than canned beans (and far more time consuming to prepare). Lentils are another option as suryadaya said but they are more expensive I believe.
Of course, pasta, potatoes, oats, and most grains are cheap (go for whole grains if possible, usually they are insignificantly more expensive). Frozen produce (v.s fresh) and in season produce are cheaper and I tend to find ethnic groceries are cheaper for some things than many regular groceries.
Another possibility to save money is to grow some of your own food. There are a variety of ways to grow herbs and veggies indoors and, of course, if you have the land for it you can grow outdoors. Some pretty interesting ideas I have found include wooden palette vertical gardens and miniature window hydroponic gardens (like those detailed at windowfarms.org).
Finally, and I may get some bad reactions to this, there is the possibility of dumpstering; salvaging food from dumpsters. Many restaurants, groceries, convenience stores, ect throw out perfectly good food on a daily basis, food that would otherwise go to waste. Many of these foods are simply nearing their expiration date and many are sealed, keeping out harmful bacteria they may pick up in the trash. Of course, there are safety measures and laws to take into consideration but it is a completely viable option. Heck, dumpstering is a good way to salvage many useful things. If you can get past the ingrained idea that such a practice is dirty, gross, or dangerous then there is a wealth of food to be had (and a wealth of info about it online). One man’s trash is another man’s feast.
