What sets the SSL monitor apart is that it can also monitor other services which transfer data securely over SSL. These include FTP, SMTP, POP3 & IMAP. It is a lot cheaper than HTTP monitor because it does not send HTTP requests.
Monitoring an SSL certificate with Pinger Man costs as low as $0.0375 per month.
We also introduced the concept of Low Frequency monitors which run once per day. Our WHOIS monitor had it's own quota that was not shared with other monitors. We put similar monitors such as SSL & NameCheap in this category to provide the same cost effectiveness to our users.