While there are many challenges associated with being a vegan (just what can you get at McDonald's besides an iceberg lettuce salad?), budget grocery shopping is not one of them. Sure, tofu can add up, and if you insist on buying dozens of Boca Burgers each week, your budget may suffer. Yet compared to the cost of eating meat and buying cheese, vegan shopping is cheap.
I distinctly remember a $15 a week grocery budget in college. If I had to buy even a pound of meat with that, it wouldn't have gone very far. Yet I was able to buy several pounds of tofu from the local Oriental food store (at a dollar a pound), a 5-pound bag of whole wheat flour ($2.79), a couple of pounds of fruits and vegetables (anything that was under a dollar a pound), and plenty of noodles, spaghetti sauce, TVP, dried beans, split peas, and lentils. It definitely wasn't very fancy, but it was healthy and inexpensive.
Boca Burgers and vegan cheeses were splurges; while they were definitely less time-consuming to prepare, I had a lot of time and not much money. A couple of times a year a relative would take pity on my poor grocery budget and give me $20 to spend on vegan chocolate and Follow Your Heart vegan cheese. Needless to say, after several months of TVP and nutritional yeast based "cheeses," I was very thankful.
I spend a little more each week now for food; I now eat a lot more fresh fruits and vegetables, and fewer canned ones. I have access to a discount grocery store, which is heavenly! I can get my splurge foods for just a fraction of the cost. This would have made a huge difference when I was in college, but I definitely got by all right on what I had.
Vegan grocery shopping, when done right, is probably one of the cheapest ways to shop. If you view prepared, packaged foods (such as Morningstar or Boca Burgers) as a splurge rather than an everyday food, you will spend just a fraction of the cost of what you would on meat and cheese. However, it really comes down to making the bulk of what you eat at home, from the raw ingredients. Vegan packaged food is expensive! Eating well on a vegan diet is not.