What about different technology tiers being able to extract refine materials to a certain degree? Like all iron is the same iron, but depending on what level of refining you are capable of, how good your technology is, you can refine the same material but to a much better degree than others. That way, everyone has access to most materials from the get-go, but it just may be not even worth the time for large-scale extractment of most resources.
Additionally then, if you also add in different types of the same material along with what I said earlier, it would make the resource industry quite diverse.
What I'm saying has probably already been thought of, but one thing I would definitely like to iterate with this is give materials at least two properties. Then make it so that if you want a good value with one property, you have to sacrifice another. That way people don't just get the best refining equipment and the best type of each resource and stop there and make that an end goal. Otherwise it'll take people 10 hours to reach that, and then they'll have the perfect equipment for the rest of the game. Make it so that there isn't a "perfect setup" and then it will create a more diverse market with no end goal.