A vegan diet is easy if you're coming from an already health-conscious diet, meat or no meat. Before going vegetarian/vegan, I was already paying attention to what I ate, cooking at home for almost all of my meals, and generally educating myself about nutrition and diet.
Going cold turkey from the kind of person who eats out for most of their meals, or generally doesn't cook much from scratch, to the kind of person who cooks their own meals using plant-based ingredients is going to be difficult, no matter what. Not only do you have to learn about what kinds of ingredients and recipes are at your disposal, you also have to get good at cooking (which is not just some skill you are either blessed with or aren't).
My wife & I live in a medium COL city, and eat a vegan diet for 2 with plenty of splurging (both w.r.t. $ and health) and very good nutrition, without breaking the bank. I'd say including our spending on treats or non-homemade convenience ingredients like Beyond Burgers and the like, we spend around $100 a week for 2 people and eat like royalty.
With a little bit of effort, I could probably reduce that spending by about half, and still have a variety of meals (ranging from asian stir fries and thai curries to BBQ and healthy pasta).
To anyone trying to get started, I'd say the main things to look into are:
* Legumes. Beans and Lentils are versatile and dirt cheap if you buy dried. We have an instant pot that makes cooking them even easier, but you can get by with just soaking and a pot on a stove.
* Vital Wheat Gluten & Seitan. I don't mean store-bought Seitan (though it's good, it's very expensive). Buy some vital wheat gluten at a health store or on the internet, and make some seitan meatballs, sausages, anything. It's an excellent source of protein, and you can do so much with it.
* Tofu. There are a few different kinds of Tofu, as well as other soy products like Tempeh (fermented soy). Tofu comes in such varieties as silken (very soft, used to make stuff like vegan cottage cheese, or in baking), firm/extra-firm (used for stuff like stir fries or baking), and if you hit up your nearest asian market, you'll find a bunch of others like already fried tofu, tofu skins (yuba), etc.
* Nutritional Yeast. I use it in a lot of ways, but it's basically a cheesy/nutty seasoning. It's definitely a staple. Try it on avocado toast.
* Veggies. Figure out which veggies you like and how you like them cooked. Roasting is a good go-to for most. Get a variety of color, and check out your local farmer's markets, CSA/Crop-Shares, or local farms for cheaper produce.
* Cheese made from nuts. You can make homemade cheeses using cashews. This is more on the "I miss cheese" side of things than health, but I mean, it's cashews, it's not artificial or anything.
As far as health, nutritional science changes it's mind about certain things every so often. You can see the general consensus flip from "Eggs are bad" to "Eggs are amazing", and this happens with all sorts of things. People used to avoid fats, now they try to eat fats. I personally try to limit my carb intake, but I'm not gonna feel bad if I eat a certain amount of carbs through legumes or non-starchy vegetables. I have a protein target I try to hit (which is pretty easy to do especially using seitan, peanut butter, nutritional yeast, and other such protein-packed goodies), and I don't go over a calorie limit, and that's all I track when I track. The mix of carbs to fats varies day to day and it's been working for me. You might feel better with extremely low carbs, or you might not ever get many fats.
It's also not a requirement that no one eat any meat or animal products ever. Before going vegetarian I was "flexitarian" and would occasionally eat meat when I was out and about. Now I eat mostly vegan at home, but when I'm out I sometimes get something with eggs or cheese. The current rate of meat consumption is not sustainable on an environmental level, even if you don't care about the ethics.
But it looks like I've rambled on for long enough. I just wanted to point out some of the ways a vegan diet is accessible both from a cost and a nutrition stand-point.