I like the tiered approach to bar cost reduction however, going down to 800g a bar to produce would leave the profit available per bar at 700g/1200g which is to high and no refining process is that efficient, the lower price should ideally sit at most half the initial cost?
If you used 3.5% from 11-15 and then 5.28% from 16-20 you could get down to 1,100g/bar at level 20. Then profit at 12k bars day is 1.7b/3.9b a year at max output.
I don't think break even should be reached in the same time frame as it was with warehouses, the profit margin there is negligible compared to the profit goldsmiths could make. I think with this care needs to be taken If the ability to make to large a daily profit comes from goldsmiths then it could potentially destabilize the economy in the game.