100 apples equals about £36.I pressed (the small press kind) 5 Royal Gala apples, and only got about 250ml juice. Worked out that id need about 100 to fill a Gallon demijohn if I use Royal Gala (which I wont be, I'm waiting for summer to get some good apples, but I'm not sure whats the best available variety in ireland and also best value for money)
It probably also depends on the ripeness of the apple, size of apple and the brand.
Most of the videos say to food process the apples and then press them.Apples for cider don't have to meet the cosmetic criteria for apples at the market. They can also be left longer on the tree to ripen better. If I can get 5Litres per 10 kg from my homemade press, a proper cider press should be able to do better. The apples have to be milled first to make pomace, a coarse kind of puree, then wrapped in muslin cloth or mossie net to make the "cheese". There are some good videos on youtube which show how to do it.
But a food processor doesn't get as much juice so you end up spending much much more on apples.If you use a basket press with the slats you don't need the cloth.
If you are just doing small quantities a food processor is fine.
If you do some research with google and youtube you will see the difference between a basket press and an apple press.