So long as you own a non-pirated copy of Windows 7 or Windows 8.1, then Windows 10 will be a free upgrade for you when it comes out. For everyone else, purchasing a retail copy will be their only (legal) way of obtaining Microsoft’s new operating system, and according to a recently leaked store page from Newegg, Windows 10 will cost $110 or $150 depending on which version you get and will launch on August 31.