Although I’m not sure which specific “site” you’re referring to, perhaps this link from ISSA’s website has the information you’re looking for:
If you look at the column on the left, you’ll see that the certification costs either $499 or $599 (depending on how you pay). The rest of the page contains more information about some of content that’s covered with the Senior Fitness Certification.
I hope this helps!
Another Senior Fitness Certification that you should consider looking at is Healthways Silversneakers program
Cost of these workshops are: $40.00.
They have a new program called “Flex”.