Battle for Azeroth, World of Warcraft's next expansion, will be launching on August 14 with a base price of £40 / €45. The base game, along with all previous expansions (including the most recent, Legion), are now included in the game's subscription, however. So, regardless of whether you bought the game, a few expansions, or nothing at all, you can play the full game and expansions (excluding Battle for Azeroth) as long as the subscription is active.
It's worth remembering that a World of Warcraft subscription is £10 / €13 per month.
Blizzard has also released the pre-release patch, version 8.0, adding several new features into the game, including some exclusive to those who buy Battle for Azeroth, while others are available to all players. The video below will let you know on what's included in the pre-release patch.