What sort of fruit and veg?
Carrots, onions, turnip, swede, UK greens/cabbages, celeariac in season beans, potatoes = cheap
Asparagus, 'kale', washed spinach, rocket, salads, fancy toms, mange tout etc = more expensive
Same with fruits, you cant expect to have things that are fancy fruits and it be reasonably priced.
Anything ready wrapped, normally more pricey. Having said that, our greengrocers is extremely expensive, we only shop there when we want to spash out.
Bulk out with pearl barley, rice, potatoes, lentils, chickpeas etc etc
And as others have said, make massive stews, slow cooker, very slow cooked casseroles.