$39.99 for the non-subscription based game
Buying the game will grant you full access to its content, without a subscription fee. The only real paywall are the free-to-play esque items that you can buy from the in-game shop, which aren't really required, and are mostly cosmetic.
As I've said many times before, I enjoy jumping back into Guild Wars 2 sporadically, as I don't have to worry about a fee if I just want to check out a new patch or play a few rounds of PVP. In that regard, it's a pretty easy sell to people who are already MMO fans.
Guild Wars 2 [ArenaNet]