1. $6000/year, OR
2. link-back, OR
3. If neither of these options are chosen within 3 months,
we will disable the service on our end.
The $6k/year price is a bit steep, but that's their prerogative. Similarly, they are well within their rights to disable the service after reasonable notice. They may even be within their rights to sue, but suing clients (or even threatening to) is not the way to Win Friends and Influence People.