Markets if you have one can be cost effective but you do have to eat the fruit quickly. Supermarkets if you go regularly and get reduced stickered fruit and eat that day can reduce cost.
I don't have time for that so buy frozen for mango and pineapple plus berries except strawberries as unless I blend them they don't like them frozen (too slimy).
Buy as seasonal as you can will get more for less with fruit.
If you can stretch to a few pots and some soil plus some plants you can save money by planting your own berry plants in the longer term.
My strawberry plants, blueberry bushes in pots gave me loads last year. Raspberries can have a long fruiting season too but best planted in a bed for maximum yield and they can spread sideways a bit.
Has saved me loads as my kids will eat a punnet between them in minutes.
They don't need 5 fruits a day so up the veg options that are generally cheaper and offer limited fruit options per day.
Also tomatoes, cucumbers, peppers, squash, pumpkin, green beans, peas, avocado, aubergine and sweetcorn are technically all fruit if they argue about not having enough fruit!