Thanks for the chapter.
The economic benefit of a dungeon that allows you to exploit it beyond random battle loot is an interesting proposition. Farming and mining on a large scale on an area of 'unlimited' resources would completely destroy the current economic order. But you'd need thousands and thousands of Adventurers dedicating themselves solely to mine and farm an area to gather enough resources to make it worthwhile. And depending in what state the mineral or organic loot came in, it would also turn greater profits than traditional farming or mining. If all they have to do is kill a certain creature on a certain level to obtain, oh, say, 1kg of iron, then if they get it as dirty ore or refined iron ingot would immediately crash economies worldwide as the dungeon iron would be in a ready state to sell right away. Or if you can hunt down an Ent-like creature to obtain wood, if it came in the shape of an unprocessed tree or actual planks would determine on how useful the new dungeon-sourced materials could be and how ready for sale they'd be. And now, think about being able to do the same to obtain grain or vegetables, grown, refined and ready for consumption. Food that can literally make you stronger, smarter, faster, etc? It does my head in when I think about it and remember how farming was treated in WoW for example.
Also, if an area in a dungeon is left unmapped and you try to restrict access without a clear explanation, then dungeon explorers are going to make their way there out of sheer curiosity or greed.
that does really depend on what it's possible to mine, and what do you need to do to mine it: iron, for example, is one of the materials that most certainly wouldn't even make a blip on the exchange rate graphs.
Let's assume that it will take 5 minutes to kill a monster and it will drop 1kg of steel rebars (I didn't find a spot price for cast iron); let's assume that ALL of the 100'000 adventurers dedicate ALL of their time to farm steel, and that they will do it at the average japanese salaryman rate (10 hours per day, 6 days per week, no vacations). They would amount to 0.3% of the global steel production.
And then there is the matter of cost. People diving in the dungeon will need proper training and proper equipment, meaning that they will also command an higher salary; according to salaryexplorer.com, the median JSDF soldier takes 382'000 yen per month, or 31'000$ per year (a little less than 10$/h, at the rate we would work them, the average US miner salary is 25$/h). This means that 1kg of dungeon steel would cost, of mining labor alone, 0.49$/kg: the spot price for steel rebar is 0.48$/kg. And we didn't even factored the logistic of the whole operation: how whold you take the tons of steel out of the 20th level? Who would do that? How long would it take? How much would you need to pay them?
Rare and expensive metal like rhodium COULD make more sense: a single kg is worth almost 458'000$, and since the world yearly production is only 25'000kg, dungeons COULD affect that particular market. On the other hand, the rhodium global market is worth only 11B$ (exactly because there is so little), so, even if it get disrupted, no big loss. You should also consider how hard it would be to reach the mining places: MC, which is insanely OP, hasn't even reached level 20, the bare minimum to start, and we are talking level 60-80 for the rare stuff.
The food isn't even worth considering: the yearly global production of corn alone amounts to 1'218'568'000'000'000 kg.
Or you could spend your time looking for magical abilities and potions that regrow limbs. Just saying...