Alright just listen to how absurd this is.
So you can exchange 15 treasure hunter keys for 1 whole bond which gives you 15 days of membership.
The funny part is that you get 1 treasure hunter key just for logging in daily.
But members get 2 treasure hunter keys daily.
So you play for 15 days normally, use your 15 keys to get a bond.
Now you play 15 days with membership and get 30 keys.
Buy 2 more bonds even.
Keep doing this till you're paid for the whole year.