$5.99 for NWN Diamond alone and as low as $1.99 if you buy others. Only this weekend though. Lots of good stuff there for $21.10
And for new folks who missed this...
Subject: Why can't I log in? / Alpha Server FAQ
PlasmaJohn wrote:GOG.com keys
Please be aware that when you purchase NWN from GOG.com that it comes with a set of default keys. Even though the MasterServer is no longer operational, the NWN server software requires that all players connecting to it must have a unique set of keys. We have blocked the default keys to prevent issues.
GOG will supply their customers with a unique set of keys suitable for multiplayer use. Please visit this page to request new keys: GOG Link