I always find that the first few times you try to make a change it's really hard; but once you get into the habit of it it's much easier. I used to work in an office with a constant supply of cakes and biscuits and I never thought I could avoid it. One day I made the decision to stop, and it sucked for a bit, but then it became a lot easier.

I understand about not having much money either, but I tend to just avoid buying junk foods, so if I REALLY want it I have to go to the shop to get it. I generally cut up cucumber and celery and have it with salsa or houmous if I want something with a crunch. It seems daunting having to prep food, but I think I actually save money by doing it- I also throw away a lot less now so less money wasted in the bin

Motivation is what gets you started. Dedication is what gets you there. I say this because people expect to have tons of motivation for their journey all the time and it's just not realistic. Like most days I feel like giving up and just sitting on the floor with all the chocolate I keep in my fridge and having a good time. But I don't because it's not going to get me where I need to be. If your reason for doing this is not greater than you want for your bad habits then no amount of 'motivation' is going to help.

You don't have to be a super fresh clean eater to be healthy it's a very elitist monetary thing to eat only 'clean' foods. I eat a lot of pre-made and pre-cooked food, like quiches and tinned curries, and I lost a lot of weight doing it, you just have to be aware of your portion size. You and the food scale are about to become best bros. But yeah, see what you have in your house and your freezer and what you can make out of it. Can you make more than one serving of it? That's two or more meals right there. Basically if you make one of something, if you can make another one at the same time then you cover it in tin foil for the next day, that's meal prep in a nutshell. Makes life so much easier. I'm a sucker for oatmeal. I eat the sachets with all their sugar and crap that people moan about but a box of 8 sachets is a week's worth of breakfasts sorted. Especially when they're on sale and I bulk buy. One of my favourite things, dinner wise, is I get a tin of minced beef, usually with onions or something and I put it into a baking dish, add a few frozen peas and then I put some premashed sweet potato mash or root vegetable mash (rutabaga/swede and carrots) on top, cook it and call it sheperd's pie. It's three good helpings for about £3.50. I mean, I could mash my own sweet potatoes but sometimes I just don't have time. The best thing anyone can do is plan their day. You can't be tempted away by the extras if you know for lunch you're eating X and then you're eating Y for dinner.

Exercise wise, if you're looking to tone up then you really want to be in the weights section, free weights (dumbbells) are great for beginners. Cardio should supplement your weights and improve your cardiac function but it won't give you the lean look. Just the skinny fat one. So don't get too caught up in it. Definitely take classes they're great fun and bring a sense of community to your workouts. You might find something you really like that way.

Anyway I've rambled enough, I hope some of it, if any, helps.

I'll be brief, but as @aprilb1304 said, making it a habit is the best way to ensure you'll be constant at eating good food. Once you start feeling the results of eating healthy (your stomach's digestion, less bloating, energized..) you will want to keep it up. With junk food I use the same strategy, I try not to keep it on hand so that I have to go out and buy it, which makes you think twice about it. I do have some nice snacks because when you have a craving, you should have something to fill it with, but I find that choosing something extremely healthy instead will not satisfy the craving so I will eat both in the end. If you buy yoghurt in larger portions it's usually cheaper, and if you mix it with some granola and fruits it's a sweet, crunchy and filling snack.

For breakfast, you can find pretty cheap oatmeal, just boil it with milk or water for 10 minutes and add in nuts, fruits, seeds, cinnamon and stevia/honey/sweet of your choice. Cheap protein sources for lunch can be canned tuna/sardines/salmon, eggs, chicken thighs/breast, cottage cheese...pair it with affordable veggies and then cook a large batch of carbs at the beginning of your week so you can distribute onto each of your dishes (rice, sweet potato, quinoa, wholegrain pasta occasionally..). Just add some seasonings or light sauces to make it savory! If you need any ideas feel free to hit me up, good luck