If you’re one of the 20 million(!) players who have the PC edition of Minecraft (referred to by techy people as the Java version) you’ll be able to download Windows 10 Edition Beta from the Windows 10 store for free. Other players can get it for the paltry price of $10 during the beta period (the length of which is still being decided).
The “Minecraft: Windows 10 Edition” beta will be available for download in the Windows 10 Store beginning July 29. Players who already have the PC edition of “Minecraft” will be able to download the Windows 10 beta version free. Others can download “Minecraft: Windows 10 Edition” at a discounted price of $10 throughout the beta period. Players who download “Minecraft: Windows 10 Edition” during the beta phase will still have the game when it comes out of beta, and receive all future updates to the game at no additional cost.
https://mojang.com/2015/07/announcing-minecraft-windows-10-edition-beta/