I think even the wealthiest mercenaries don't pay that much for their gear
I think if you add up all the milspec equipment a mercenary group has, you might be surprised. But I could be wrong.
I'm not likening adventurers to real-world mercs. I am instead making a point about economy - people say all the expensive stuff PCs have breaks the economy, and I am not sure that's true.
In the real world, there's a whole lot of very expensive equipment that you don't think about. Garbage trucks aren't cheap. Neither are dentist's drills, or MRI machines. I'm in a Boston suburb, but within a couple miles of my home are a hospital and a university with research scientists - there's hundreds of millions to billions of dollars of equipment that I don't normally see or think about. Out of sight, out of mind - that stuff doesn't enter into my consideration when I think about "the economy", but it most certainly is part of it. Far, far beyond the buying power of the average individual person, but it is still there.
While it is put to different uses, and is funded differently, the adventurer's gear is like that very expensive equipment.