Transferring data to the https protocol is not as simple as it may seem. From what I have read, you will need to purchase ssl certificates (they are not cheap) and the entire website would be under the https protocol. A brief article about the certificates of the https protocol can be found at http://www.entrust.net/certificate-https.htm
However, you may be able to make a deal with your web host about these certificates and if that is possible, it would be the logical thing to do. That covers most of the basics of the https protocol and isn't that greater deal to use it from my point of view. Also could I ask why you want to use this protocol as it only prevents man-in-the-middle attacks. I would have to say there is a lot of other inexpensive things you can do to secure almost any php website. Example: Filter $_GET array to remove malicious data that can delete your website.