During this year's Minecon, Microsoft announced that Minecraft: Windows 10 Edition is on the way, and that existing Minecraft players on PC will be able to upgrade to the new version for free when the beta starts on July 29.
The new edition is built around the new feature-set of Microsoft's incoming OS, Windows 10. Existing players will get it for free, while new players will have to stump up $10 to get the game and access the beta (after the beta it sounds like the price will go up).
It's also worth noting that Mojang has confirmed that the new version of the game won't replace the old one, and both will be supported equally from here on in. For more details head to Mojang's blog.