I made my first few batches by pressing the apples myself -- a lot of work but rewarding. There are several YouTube videos that show how some people have done this.
I cut up apples, chopped them up with a kitchen blender and put the results in a nylon bag. You can use any method that will break up the apples enough that you can get most of the juice out of it.
To press, you can buy apple or wine presses ready-made, but they are expensive. I made a press out of 2x4's (normal wall-framing wood), mostly following the instructions in the book "Real Cidermaking on a Small Scale" by Pooley and Lomax, ISBN 9781854861955. For the tub I used a big 5-gallon pail (like paint comes in) with holes drilled in it.
My math was similar to yours -- it took about 120 pounds of apples to get 6 gallons of juice. The smaller the apple is chopped up the more juice you'll get.