It really depends on what you're trying to do and what food costs are like in your area. I live in the American midwest and usually buy meat that's on special so 1.99 for boneless skinless chicken breasts, 99 cent a pound drumsticks, and so on are pretty hard to beat. Way cheaper than tofu or polenta or any of the vegetarian/vegan stuff that's thrown into the specialty aisle. My grocery store pretty much never offers vegetarian stuff as a door buster. Now if you're doing beans and rice, veganism is definitely cheaper. Even grilled cheese or mac and cheese tends to be cheaper than meat meals, although that's more vegetarian than vegan.

I'm not a vegetarian by any means but I like to stick to not eating meat besides fish on Fridays during lent, so this is the time of year I start to get aware of other lifestyles. Growing up we always ate fish, but as I became an adult I realized how expensive that was. Even the craziest vegan/vegetarian meal usually tends to beat fish in a contest hands down. My family thought I was weird for eating vegetarian when I was "allowed" to eat fish, but I'd rather have a veggie burrito at chipotle than a filet o fish even when the filet o fish is cheaper. (I really miss fish mcbites... it was the perfect lenten option for crazy picky eaters who really liked chicken mcnuggets. Sad it didn't stick around)

I guess the most important thing is getting out of the American mindset that you need a huge chunk of meat for every single meal. Or that "chicken every day is boring." Reducing meat is a great way to save money. I was really naive for assuming in the past that anything without meat was automatically cheaper, but food pricing is weird.