Taking myself for example:
Heavensward: $129.99
Subscription from June 23, 2015- June 20, 2017: 24 months x $8 (legacy) = $192
Total: 321.99

^ This is just to play the game.

Add in retainer service which is $288.00 for 6 retainers over 24 months.
Total for me to play the game as I choose: $609.99