The best al around resource is the PPH (Peaceful Pill Hand book) that has all the details from a medical and technical point of view, page 129:
https://gofile.io/d/W0Zwnc
Exit bag diagram: (scroll down to the mechanism section)
https://en.wikipedia.org/wiki/Suicide_bag
Also some good posts by SanSui members include detailed photos of their systems:
https://sanctioned-suicide.net/threads/leaving-in-an-hour-goodbye.187099/
https://sanctioned-suicide.net/thre...ng-together-a-nitrogen-exit-bag-setup.187337/
My own system with out the exit bag:
What I bought (I'm not from the US so I converted to USD):
For gas flow:
Nitrogen tank containing 600 Liters ($140)
Regulator + Flow meter that connects to the tanks threading ($55)
Pipe for Nitrogen flow from flow meter to exit bag (2 meters) ($5)
For Exit Bag
35x50 cm Oven bags for assembling the Exit bag ($1)
Porous tape for taping the edge of the bag ($1)
Elastic underwear rubber band ($1)
For calculating the volume of the Nitrogen compressed in the tank you need to know the volume of the tank and the pressure. You can read the pressure from the regulator/flow meter. The recommended flow rate by the PPH is 15 Lt/min for 30 minutes. That requires 450 Liters of Nitrogen.