I’m happiest that I built the gift shop at Jericho Locks as a very specific set of circumstances allow it to be the best area in the game for me to get Hinterland Scrip right now. You can sell an Infernal Sharp Shooter’s Rifle at the gift shop and it gives 450 scrip at max train luxury. I can make the rifle at my lab by getting 26-30 research an action by combining Lettice and the Smith from the Nemesis Ambition which means getting a rifle takes 63-70 actions.
This ultimately means I’m getting around 6.4 to 7.1 scrip per action. I’m not sure if Bone Market shenanigans can get more right now, but this is the simplest method for me so far.