It’s perfectly doable and will be easier if you stick with fresh produce and homemade meals.
Breakfast – think porridge, scrambled eggs, yogurt & fruit (big bag of frozen fruit), smoothies
Lunch – think homemade lentil soup, choice of protein and salad
Dinner – think stir fry for quick meals, casseroles, stews and anything you fancy that can be bulk cooked and portioned.
On that sort of budget and low calories (for a big guy) then if you focus on getting in your required amount of protein into your menu for the day, just bulk the rest of your calories out with as much inexpensive vegetables as you can. Carrots, onions, spring greens and courgettes are all good. Potatoes, sweet potatoes, brown rice are all good to add for carbs. I would stay away from pasta, too much calories for not enough fill IMHO.
One of my favourite meals is just a chicken breast sliced on the angle into three pieces placed on top of a load of sliced chunky veg such as carrots, courgettes and sweet potatoes with some olive oil drizzled over, some black pepper and herbs and roasted in the oven. Doesn’t costs much, well under 500 calories and most importantly for a big guy is actually quite filling.
You can make a big pot of lentil & vegetable soup – one very large onion, three or four sticks of celery, four or five large carrots, two courgettes (or swap for something else), 350g red lentils, can of chopped tomatoes and make up to 4.5 litres with stock. I do this on a Sunday, portion into seven plastic tubs, three in fridge and four in freezer and that is my lunch sorted for seven days for pennies.
If you need help tracking your intake and what calories are in what foods I can recommend Nutracheck.co.uk – it was an eyeopener for me and it helped me drop about 8 stone a few years ago.
