The answer is 4,400 cranberries per large container (gallon) of most cranberry juices.
That is a lot of berries.
If they were picked by hand (dry harvested) then a gallon of cranberry juice would likely cost $100 or more due to labor alone. That price is just a guess but most people wouldn’t be buying any if they were hand picked.
Cranberry juice comes from wet harvested cranberries, the ones you see floating in the water and they are scooped up in large quantities by machines that get them ready for processing.