Trade Prices desperately need a rebalance
I've searched around and I'm sure that it has been mentioned by this point but I didn't really find anything of note on the subject, but the trade prices in this game make absolutely no sense. It costs more for the raw materials than what you can sell the finished products. There is little reason to ever make a finished goods production building besides simply having an over abundance of raw materials.
Example: Gold Bars. It takes 3 coal and 6 gold ore to produce 1 gold bar at a Gold Smelter. Base selling price of Coal is 1 gold. Base selling price of Gold Ore is 4 gold. Base selling price of Gold Bars is 7. So you actually lose 20 gold by trying to produce gold bars. That's not even figuring in the monthly expense of the Gold Smelter.
Example 2: Jewelry sells for 10 gold. 1 Gem and 1 Gold Bar cost to purchase is 30 gold.
In almost every situation, it's actually better to simply purchase the finished goods than try to make anything yourself. The only limitation here is the amount you can purchase at one time.