When discussing the price of Windows 10 most people fixate on the idea that it will be a free operating system. The reason for this is that to upgrade a Windows 7 or 8.1 PC it will be free, and upgrades going forward will be of no charge. This does not mean that Microsoft is not selling Windows 10, simply that most people will not directly buy it. For brand new machines, or machines with an OS other than 7 or 8.1, you’ll need to buy a copy of Windows 10.
The prices for Windows 10 are more or less in line with the prices for previous versions of Windows. For the Retail versions Home will be $119, Pro will be $199 and an upgrade from Home to Pro will be $99. For the OEM licenses Home will be $109 and Pro will be $149. To put this into context it is the same price they are currently charging for Windows 8.1 Retail, and $10 more than they charge for 8.1 OEM.
Since the price is so close between Retail and OEM I would highly suggest most system builders think about buying the Retail version. As far as licensing goes the Retail version allows you to legally move your license between physical machines. So if you toss your old machine and build a new one you are within your rights to reuse the license. For OEM the license stays with the physical box. If you toss the PC you need to buy a new license. I know some people will brush this off, but remember that Microsoft’s activation software has been getting progressively more strict. An extra $10 for the Home version now may well be worth not dealing with frustration later.
See Microsoft’s statement to Neowin here: http://www.neowin.net/news/microsoft-windows-10-home-costs-119-pro-costs-199