Actually junk food is more expensive if you take into account what you actually get for your money. What junk food IS in comparison to "real" food, is quick.
Rather than try and turn everything around at once, why not start by making a few changes, get them established in your life, and then add a few more?
The sausages, kievs and sausage rolls will be LOADED in fat, pretty much devoid of any actual protein (they tend to use a tiny percentage of meat and then lots of flour and water to bulk it up). So you really should give them a very wide berth.
Aside from stress, IBS is normally attributed at least in part to fatty foods, processed crap (like crisps and biscuits), chocolate and fizzy drinks. Since most of those things seem to feature quite prominently in your diet, you may well find that your IBS improves as your diet does.
Firstly I would recommend that you not use butter on your toast in the mornings. One single tablespoon of butter is over 100 calories and almost pure fat. Obviously use it up, but when it comes to replacing it go for something like lurpak lightest (or do some research - go for something without hydrogenated fats or oils). You can also try switching to wholemeal bread, which will keep you full for longer, as it takes longer for your body to digest (white bread is converted to energy at almost the same speed as pure sugar, which means you get hungry quickly after).
Don't snack on crisps and chocolate in the evening. It's pretty much a vicious circle - emotional eating aside, you're probably at least partly hungry later on because the kievs and stuff you eat aren't going to keep you full for long. But the money you save on not buying the crisps and chocolate gives you a little bit more to spend on decent food to eat at mealtimes.
I think cooking in bulk is going to be your friend. It saves on money, because you get a good few uses out of one batch, and there's no wastage at all. A batch of vegetarian chilli is going to fill you up, last longer, be 100% better nutritionally for you, and come out at pretty much the same price as some of your frozen stuff. Same for a big batch of lasagne.
The only thing I'll say in relation to your aversion to vegetables is this:
- Vegetables are very high in fibre, which - when you are not used to it - can cause you constipation and indigestion AT THE BEGINNING. High fibre diets are recommended by pretty much everyone and his dog as being extremely healthy and can even help to avoid certain types of bowel cancer.
- Vegetables are very versatile and extremely cheap. They are a brilliant and cheap substitute for meat, they are low in calories, and they are brilliant for your health.
So if you have had an actual doctor tell you to avoid vegetables, then fine. But if you are self diagnosed, then I'd really urge you to start to slowly introduce them into your diet.
On the depression, I take it that you are already seeing a doctor about it, and have been given either medication or some sort of guidance? Whilst I in no way think that it is some kind of "magic cure", I would really recommend that you start doing some form of exercise on a daily basis, which has been proved time and time again to help manage depression. Even if you start off with a brisk 30 minute walk on a daily basis and work your way up. I'm not saying that it's a panacea, but it should help, and it will have the added benefit of helping you to burn calories.