I'd provide the less expensive stuff, apples, pears, bananas, and things on the discount stuff, stuff in season etc.
But I suspect if you could stop him eating quite so much sugar in the form of fruit (which really has got whopping amounts in it, the amount of insulin I need to inject to eat fruit is huge and the speed with which it increases my BG, wow.) and filled him up on more fibrous veg and slow release carbs, you might find he is less hungry.
Even in a slim healthy person that sugar will spike BG and cause a crash, in a non diabetic that spike might not be dangerously high but it still causes peaks and troughs, the troughs leave you feeling ravenous... and so there goes your half a pack of crackers covered in jam which spikes BG... and hes full for five minutes.. and then it crashes and off he trots to the bottomless supply of Mums food again...
Brown bread, protein, lettuce, salad leaves, peppers, cucumber, sweetcorn should all fill him up more (and neatly, make great sandwich fillers).