SSL Certificate

Use an open-source util called OpenSSL if you want to make one yourself (self-certifying), it's free.

Or you could use a crowd such as Verisign or Twaite.

Here is some of the information I read up on when checking this out for my project at work

<snip>
http://www.nurdletech.com/https.html

http://www.linux-sxs.org/internet_serving/apache2.html#MOD_SSL

http://www.webopedia.com/DidYouKnow/Internet/2005/ssl.asp

http://www.redhat.com/docs/manuals/linux/RHL-7.3-Manual/custom-guide/ch-apache-secure-server.html
</snip>

We used self signed ones as we would have needed multiple certs from a CA.

However you would only need one since all clients would be accessing your site online.

Have a look at the first link. It mentions a Certificate Authority that don't charge. CA-CERT is their name.