Microsoft has been very quiet about the pricing of Windows 10, and Kevin Turner has explained in December that the company will most likely reveal monetization plans early this year.
A document published on Microsoft's OEM Partner Center site sheds more light into how much money the Redmond giant is making from licensing Windows 8.1 to manufacturers of Intel-based tablets.
In April 2014, Microsoft announced that it will provide OEMs with a free version of Windows called "Windows 8.1 with Bing" for devices smaller than 9 inches. From the table you can clearly see how Microsoft defines "free", and the configuration discount means that OEMs are required to set Bing as the default search engine in Internet Explorer (users can still change it) as well as MSN as the home page (can be changed later).
Windows 8.1 with Bing is listed as costing $10 per copy, but is offered at no cost to OEMs that make devices under 9 inches, which lowers the expenses usually associated with licensing the operating system. Even larger devices benefit from a $10 "configuration discount", lowering the licensing price to just $15.
To help grow the market of Windows devices, Microsoft also offers an additional SKU called "Windows 8.1 with Bing and Office 365 Personal", which is a low price offering that includes a free, 12-month subscription to Office 365 Personal, and is also subject to a configuration discount.
The Office 365 SKU is priced the same as the normal Bing SKU, which means Microsoft is giving away Office for end users of tablets.
Microsoft may not talk about the full monetization of Windows 10 when they unveil the consumer preview, but it's likely that the company will explore other ways to monetize Windows going forward, maybe even by adding options for subscriptions built around paid services, similar to the Work and Play bundle.