The "Complete Edition" unlocks all of the expansions too, so you'll probably want to purchase this version of the game.
What is the payment model: There's a free trial which lets you play up to level 60 with no time restriction. You can also pay £7.69 for 180 days game time to unlock the full experience. The "Complete Edition" unlocks all of the expansions too, so you'll probably want to purchase this version of the game.