Why are most juices sold for the same price?
In retail stores everything is "priced" to what the targeted consumer will pay. There is little relevance to production cost to final price

The cost of most food goods is not for "growing", but the energy for fertilisers, tractors,  picking, processing, storage, shipping etc. Your finally price is mostly the cost of energy used (directly or indirectly)

For fruit juice you are paying mostly for picking (fuel), processing (electricity for water pumping and cleaning, electricity to running machines), storage (electricity), and shipping (fuel)

Cranberry juice is significantly more expensive to grow and pick, so this does show as a different price

e.g. Apple Juice. Concentrate purchased at US$1,500 to US$2,000 per ton. Reconstituted 1:5 to 1:7. So one litre of apple juice costs US$0.21 at best case. Yet you buy it for US$2+ per litre!