There are various pricing models across online sniping services. To the best of my knowledge, Gixen is the only absolutely free sniping service that is committed to stay free.
Note on the SSL field: eBay requires SSL for sign-in, so all the sniping services must use SSL to transmit your username and password to eBay. This, however, is not the case for transmission of your eBay password between your browser and the sniping service, which is what this field refers to. When you use sniping service that does not support SSL, you may be compromising your eBay password. This data is as of Aug 12th, 2013. If you feel any part of it is not accurate, please let me know.