On a fresh save (or your first playthrough), play up to Sequence 2 Memory 3 "Mr Walpole, I presume?" and when you get to the part of the mission with the optional objective to pickpocket 3 templars, do so and then pause the game, hit Edward Upgrades and back out to force a save, then restart from checkpoint. You'll keep your reales and be able to repeat this to infinium. You need around 400,000R to buy everything in the game, and I was able to farm 250k in about 90 minutes with this method. You CAN do this on memory replay as well, but some comments on the video report losing all their money when leaving memory replay, so best to do this during the first run of the memory in my opinion.
Video below, credit to the uploader for discovering this. He leaves out the Edward Upgrades section in his video, but a useful commenter pointed it out and it was the only way for me to save my money progress on each retry. Hope this helps.