Hi Pilou!
The cost to go on Microsoft Store is like the other apps store (Google Playstore or Apple Store)...in the next days we check how much, but isn't expensive.
I think that Trimble put an ight price because their software was redesigned for holographics and target high professional clients that can pay more of 1000$ to buy HoloLens. HoloLens, for now, is only a product demonstrator made by Microsoft to show the potential of mixed reality; but at the end of this year HP, Acer and others OEM will go out with cheaper products.
On the Store MoI could tray also alternative business models like free version with advertise in app and a payed version without.
I want remark that once you have published on Windows Store you can use it as your first distribution channel because all Windows 10 PC can use the app like a win32 software.

I'm new here...you are a MoI developer?

Than after this presentation of Windows Store I can go to Microsoft for give it my invoice! :-D