I want to offer a website builder.....

[lilqhgal]

.... that uses only custom designed themes that I have created myself. I want guests to my website to be able to select one of two options. The latter would be a custom designed website by me, which would be all custom tailored to their business. The main feature however would be the option for the user to sign up and build their on website using some sort of software that I already have installed on my server. Of course, I want this whole process to be automatic. Sign-up, payment, monthly billing, etc. Sort of something like how yahoo/geocities offers a website builder, or something like homestead. The only difference is that I want it all to be branded from my design company including only the templates that I will design for this specific purpose. Another thing, it's not necessary for each client who signs up to have cpanel configured/installed, as I want the website to have a simple admin interface and therefore they don't really need to see cpanel. I have WHM installed on my server for my own purposes, so whatever this program does it would need to work with that. So, my question is this:

Does such a program exist? Can anybody point me in the right direction? I've search for alot and it all seems to be offering me software (like Microsoft Front Page *gag*), OR offering me the option of building my own website (which is what I want to be doing myself). Thanks everyone!