I find fruit and vegetables cheap to buy but it does depend on what you buy. If you buy more exotic produce like raspberries/mango/cherries, especially when not in season then it will be costly.
Apples, pears, bananas,tangerines tend to be quite cheap. I can buy 6 apples for less than a pound.
Same for veg, generally carrots/cauliflower/broccoli are fairly cheap.
I keep most fruit and veg in the fridge and it will last a week,possibly longer depending on what it is.
Good quality meat can be expensive I agree. I buy my meat from an independent, local butcher and it is slightly more expensive than a supermarket. You can get some cheaper options though. His bacon is lovely and not expensive and I found a great pasta recipe that uses bacon. A beef joint will do more than one meal if you have it with veg.
Also, meat doesn't have to be eaten every meal. Fish (places like aldi/lidl do good, reasonably priced fish -things like cod and salmon fillets), eggs etc. are all good.
I think part of the issue is education around food/knowing what to buy and how to cook certain things. I came from a family of good cooks so learnt from being young but not everyone does.
Exercise can be free -walking/running for example. It doesn't have to be a gym/special class.
Portion control is a massive problem I think. If you go out for a meal, portions are often huge! There is an Italian near us and their pasta dishes would easily feed two people.
Maybe time is an issue as well? Many people work full time, often both parents, and/or long, unsociable hours which cause them to turn to junk food/ready meals.
I don't think it's a quick fix unfortunately.