I want to create a world where iron is still widely used, but is more expensive than on Earth. Small quantities would still be viable for wheel hub rings, swords, axes etc at a modest increase in cost but large iron objects like steel beams for construction would be very expensive indeed and not generally used.
I have considered using the following means: a) Reducing the availability of iron ore by reducing the number of deposits and moving those that do exist away from sources of habitation and water b) By removing coal as a convenient source of carbon in the iron smelting process (making it reliant on charcoal). c) By reducing the grade of iron ore available forcing a concentration step and making it more expensive.
Would this be workable? And if so what combination of these effects or others would work best/ be most believable? (for example roughly what grade of iron ore might work)
Background: The world is similar to Earth but with much less water / oceans and much more land / deserts. There are roughly 20 million people living across a large (1600 x1600 miles) flat area of land bounded by mountains or uplands on 3 sides and a small sea to the south. This is a preindustrial society with no steam power, gun powder or internal combustion engines, but is advanced in other respects. Other metals are also available but are not suitable replacements to iron either due to their properties or scarcity.