Eating healthily can be expensive but you get out what you put in. Would you put water in your car instead of petrol because it's cheaper? Like someone else said, you might have to sacrifice other stuff in your life but it's up to you to decide what you value more.
Fruit: apples and bananas are cheapest. Tinned fruit can also be cheaper, but get it in fruit juice and drain it - not syrup. I love berries which tend to be expensive so I wait until I see them being reduced and then buy loads, the other day in Sainsbury's they were selling blueberries for 64p a packet which were meant to be £2 a packet. So you can chuck them in the freezer and either eat them frozen, blend them frozen into smoothies, or put them in the fridge to defrost.
Veg: veg is ludicrously cheap. If you really want to eat healthily and think it's expensive, you probably aren't eating enough veg. Salad leaves are expensive at around £1 for a stupidly small bag but carrots, squash, broccoli, cauliflower etc are all really cheap. You can also buy big packs of frozen chopped peppers and onions which are far cheaper than fresh ones, and cook exactly the same as fresh ones.
Meat: butchers are always cheaper than supermarkets, near me you can get a HUGE packet of chicken breasts for £20 which would last a fortnight even if you ate two everyday. I don't eat a lot of meat so I don't know about red meat etc but again you can look for reduced to freeze it, or get a pack of frozen chicken breasts and just defrost them.
Fish: salmon is expensive but tuna isn't and tuna also has a lot of protein in.
Carbs: swap to brown. Bulk buying is cheaper. You can get big packs of brown rice really cheap, potatoes and sweet potatoes are cheap, it's just about choosing the right ones. Also lentils.
What else are you spending your money on? When I was at uni all my friends used to moan about how expensive it was to eat healthily - what they meant was, they would rather go out and spend over £50 on alcohol. If you're doing that then yeah it's expensive in total, but what needs to go is the expensive drinks out. You can buy own brand vodka and it's no different from Smirnoff etc at the end of the day, drink more at predrinks and buy fewer drinks when you're out. Plus alcohol is awful for you, my best friend put on a stone and a half at uni despite eating fairly healthily because she drinks so much, I lost nearly 2 stone with a £30 MAXIMUM food budget per week. It's doable, it just takes some effort and planning.