^^ Great advice I think 
Sample menu:
B: 50g porridge oats, 200ml semiskimmed milk made into porridge - 300 calories
L: 2 slices wholemeal bread (try baking your own if you have time!), with homemade vegetable soup (pack in loadds of veg that you've got lurking in your fridge and a can of chickpeas/some red lentils, you don't really need oil to fry the veg, just use a bit of stock to stop it sticking, make up with stock and doctor with spices) and 25g cheese - will come to about 400 cals
D: Grilled mackerel - pretty cheap, with 3 boiled new potatoes, and as much steamed veg as you like and some lemon juice(can use frozen, it's great value usually) - about 500 calories
Three snacks: each could be a small piece of fruit in season (eg: apples)/1oz of unsalted nuts/ a portion of plain yoghurt from a tub/ a glass of milk/a cup of veg soup/ 3 pieces of dried fruit - so basically about 50-100 cals each.
This would add up to a day of about 1500 calories although I'm not sure if you need more, but the point is, those are (albeit basic) VERY healthy, substantial foods which don't cost much expecially preparing it all yourself. Lots of protein and fibre in there too, as well as brilliant healthy fats from the nuts and fish which will keep you feeling satisfied. Water and low sugar squash, as well as good old tea, will also help alot between meals.
Hth!