This assumes you always have buyers for iron at $10, and and they are buying as fast as you can produce it. Otherwise you'd need a massive number of store slots to keep up.
There are two sides to any transaction, supply and demand. Supply (and rate of supply) is relatively meaningless if there is not comparable demand on the other side.
As in the real world, the most productive product is the one that you can't find for sale, and you can produce it with time, that is free.
The most difficult items to find in the Global Market;
1) Flour Bag
2) Bread Roll
3) Garden Furniture
4) Fruit and Berries
ANY quantity of the above, that you produce, will be sold immediately.
Some of those require SEEDs (25min production), other require CREAM or TEXTILES.
You can product it during the night, since they require hours to produce.
IRON is fast, but ANY ONE can produce it fast, 1 minute. I don't understand why someone would buy IRON.
