"Go vegan!", you hear, "it's cheaper, more environmentally sustainable, and just as healthy and delicious!" The problem is, these aren't all true at the same time. You cut animal products out of your diet, and what do you replace them with?

• Beans, peanut butter, lentils.
• Tofu, nutritional yeast, hummus, tempeh, seitan, soy cheese, soy milk, almond milk, almonds, "fake-meat" products.

There are a small number of vegan protein [1] options that are cheaper than the animal-based equivalent, and then there are a wide variety of ones that are more expensive. If you build your diet from the first category it's cheap and environmentally sustainable, but the limited choices mean most people won't find it as enjoyable as what they were eating. On the other hand, the second category offers enough options to suit most palates but it costs more.

And really, we should expect this. When deciding what to eat people balance taste, health, time, variety, and money. Remove some options, and something has to give. If you're willing to accept less taste and variety, you can go with beans. If you're willing to accept more cost you can go with seitan and soy milk. If you're willing to accept less time you can cook more meals at home and become an excellent cook who does more with less.

(This is a motte-and-bailey argument, where the defensible "motte" is "the cheapest diets are vegan" and the expansive "bailey" is "eating vegan is cheaper".)

[1] I'm mostly just talking about lysine here. Fruits and vegetables don't have much of it, and while Grains tend to have enough of the other essential amino acids that it's easy to get enough of those, in order to meet your lysine needs with them you'd need to eat very large amounts. For example, 12.75 cups of corn or 15.5 cups of cooked brown rice will meet all your amino acid needs, but they will also give you 7,300 and 3,350 calories respectively. Instead you need to eat some foods that have more lysine per calorie, and while beans really shine here other options are generally more expensive than animal products.