In addition to an actual simulated economy with meaningful supplies and demands and resources that fill the same need and are somewhat replaceable (will use wood not stone for building if stone gets too expensive), and blah blah, you would need additional things as well for trading to really work dynamically in the game in a challenging fashion.
For one, I think you'd need armies to be working, in the sense of being able to command and send out your own raids and to take over settlements and things like that. Otherwise you're just going to get an eye-rolling, annoying situation where some goblins are sitting on one rich gold vein, and you can't make your monopoly, because it's impossible to oust them, even if you're 50x stronger, just because the game hasn't included that feature yet. That would not be fun and it would break the immersion hard.
Secondly, I think you need some concept of trade routes. As in, settlements actually need real, passable paths between them to trade. So that if you block off a mountain pass for instance, you can control trade in and out of the enclosed valley. If prices get INSANELY high, then traders might begin risking crossing the mountains proper to get around your blockade, in a dynamic fashion, but they wouldn't for just medium value or bulk goods, for instance. Similarly, trade routes should also be able to be disrupted by devoting resources to having armed patrols or armies cutting them off (although your competitors can also assign escorts if they can afford it and see it as worthwhile). Basically a little meta/minigame where traders are like creatures and normal pathing types of things are happening, but the pathing is going on on the world map, not the fortress map.
Third, you need some way to model renewal (or not) of resources. A settlement shouldn't just be able to keep mining iron for 3,500 years in the same spot or whatever, that won't be much fun, and is also unfair/not comparable to your own fort, and breaks immersion. At the same time, this needs to be balanced with the danger of running out of stuff and having a world be unplayable. This balance can be struck by modeling recycling (especially of metals - melting down goblinite type of situation, but considered by world gen). And/or it can be struck by having dynamic "mining costs" of resources. A cost that it takes for a settlement in world gen to abstractly obtain a unit of resources from their environment. Such costs could change over time, getting higher the more you gather, but flattening out for things like trees while not doing so for things like iron. And if the cost is higher than price on the market, the entity stops mining it at all. All helping to stretch out resources longer while still making them more realistically finite or not.