SSL certificates pricing ranges from $15 to several hundreds of dollars. We won't go into the technical details, but we'll just introduce you to the pricing behind them.
In firefox 3, secure sites are color coded with Gray, Blue, or Green "Passport Officer". Gray means the site has no security. The blue means the site is secure and you can be assured that it is "safe" to provide personal information to the site. The green means the site is secure and encrypted, but also that the site has gone through Extended Validation.
The blue SSL certificate providers just validate the domain owner. This ensure the site is secure so as long as you enter in the right domain name into the browser, e.g. Entic.net instead of Etnic.net.
The green-like SSL certificate is a step further. It validates the business and confirms the owners of the site as who you would expect them to be (e.g. checkout http://paypal.com). If we had a certificate like this, our business name would show up in the certificate as "Entic Services", no one else can have this registered in their domain/certificate.
(You'll find those image boxes when you click on the Firefox site identification button next to the URL location box.)
Now the big difference between the green and the blue...
The blue SSL certificate costs $15 or less per year. You should not pay more than that. If you are, you are wasting your money. There really isn't a good reason to use this unless you run a high profile site, so don't waste your money. Remember, the blue provides good encryption and security. There is a reason Google and a ton of other companies use just the blue SSL certificate.
To find the $15 pricing, search the sponsor links on Google.
Hope that helps, if you have any questions, let us know!