Matter has a specific meaning in physics but for this purpose I’d define matter as anything that exists in the world and behaves according to the rules of physics.
We can do science to determine how matter behaves and we can determine it keeps behaving that way whether any conscious being is interacting with it. That’s why I think matter is more of a foundation of reality than experience. Experience can come and go but matter keeps doing its thing.
Certainly we must rely on experience to learn anything about matter so from an epistemological point of view it is the foundation of knowledge but I do think we can discover a deeper foundation for reality through science.
If it was useful I’d use it. Every magic item price list I’ve seen has outlandish prices I would never use, so they are only useful as rough starting points. It’s not clear what you are planning to do better than what is out there. You say the prices are exact but they are also randomized? What does that mean? Am I seeing randomly different prices every time I use the tool? And what do you mean by sliding scale? Like a UI slider widget that scales all the prices in the tool?
What I really need is a comprehensive guide to creating a gold economy for my players, along with well thought out price ranges for all magic items that fit into that economy. That’s what the DMG should have.