Hi Lianna,
The most important thing for you to know: Oreos are vegan!!
I've been a vegetarian for 38 years, but just in the past few months have moved more towards a vegan diet....more plant based. But I'm not super strict with it at this point. There are some good websites and Facebook pages for vegans. A new Facebook page just started last week for brand new vegans, to offer tips and support. The "Happy Herbivore" started it to help newbies. Just be aware that it is possible to be a very unhealthy junk food vegan.....so when you look for cook books, you might want to look through them to make sure they are low fat and not sugar loaded. Check your library for dvds and cookbooks too, but there's a ton of recipes on-line.
To answer some of your questions....it doesn't have to be expensive, depending on what you eat. It's just a matter of developing the habits and adjusting to cooking the new meal plans. I've found that it's actually fun to experiment with completely new foods and recipes. Dried legumes such as lentils, split peas and all sorts of beans are super cheap when you buy from the bulk containers. They are where you get your protein, as well as nuts, but watch the fat in nuts. Tofu is also good protein. Soak the beans overnight, cook a huge batch, then refrigerate some and freeze the rest so they will be ready when you need them. Yesterday I had a taco salad made with lentils. Today it was crock pot stew. You will probably find that you will increase your veggies, which is a great thing for weight loss. Until the last 3 months, I never touched spinach, parsnips, turnips or most types of squash. Now I'm loving experimenting with them. I eat spinach a couple times a day in sandwiches, smoothies, and no cheese/pesto pizzas, salads, etc. Never would of thought that I'd LOVE spinach! It really depends how strict you're going to be.
As far as eating out, you will learn which restaurants have food you want to eat. We do pasta or mexican food a lot. Or salad/soup bars, buffets. Thai food is often vegan. For fast food, sub shops or mexican type are the easy go-to's. Claim Jumper has a great artichoke and baked potato/veggies. Even Dennys now has a steamed veggie plate for breakfast! It takes a bit more effort, but when you get used to it, it's not difficult. You'll learn and have your favorites.
You need to be careful to get your B vitamins, (and D for me since I don't see the sun much) but you can either take a multi vitamin for B12 or like you said, most cereals give you what you need.
It's fun to experiment! I've been craving a creamsicle milk shake, so today, I put 2 oranges in my VitaMix, added a frozen banana, some cashew milk ice cubes and blended. Yum. No sugar and so good! I LOVE Dairy Queens chocolate covered cherry blizzard, so on Saturday, I made one with ice cubes, cashew milk, canned cherrys, frozen banana and carob chips. It's a winner. My freezer used to look like Baskin and Robbins so I have to find healthy replacements. Next will be Maple Walnut, made from walnut milk which has a great flavor. If you want to make your own milk, it's super easy. Choose any nut, soak for a couple hours or overnight, and use 1 cup nuts per 3 cups of water. Blend well. Strain. Add dates or whatever sweetener you choose, (I use dates and honey) some vanilla and salt. Or you can use maple syrup for flavoring. Blend again and strain. Cashews have no flavor and have a rich creamy texture, so they're good for gravy and ice cream. Almond is good for cereal. For a cheap strainer, get a nylon paint strainer from the hardware store.
This is probably way more info than you wanted, but hopefully it will give you a place to start. Btw, my teens have rebelled against this diet, but I made a vegan cheese sauce for tacos and my son ate it and didn't know it was vegan. He had seconds. That was 3 weeks ago and he still doesn't know.
Most vegan cheeses are nasty though.....nothing like the real stuff which I LOVE! Cheese and ice cream (and cookies) are why I now have to lose 100 pounds!
Good luck. Come back and post about what you decide to do.