Design a multiple site pay service

Hi
I wanna start a webservice that possible many of you have similar to or develope. Have pasted in the general idea, please give some views, tips to existing service that can be bought or if you can develope such a product or other relevant.

General idea.
I want to start a webservice that is two headed. One is that customers can register and select premade template from library. Head two is that I, admin or other with permission ceates a template and install this to clients account. It will be a subscription service and/or pay for extra service like special made template, more pages added etc.

The aim are to enter market for people that not want to pay so much for their webpage, but still needs a professional looking site. Like small business owners like pizzarestaurants, hairdressers etc. This people mostly need premade pages that they just ad their own content. Lets site have standard pages as home, about, menu (foodmenu or other; products, hairstyles etc), our team, contact. The vertical menu would then be standard. Of course admin can add extra pages etc if customer pays for it.

So, user can sign up (pay) and choose template for a premade library. He can set up his content by a easy to use administration area.

Or
User can contact site team and ask for getting made a special template for him eventually ad pages or other special features. All to an agreed price.

I have noticed that webcompanies in Norway charge a lot more than the cost of server rent, domain registration and the design of the page.

Also

To run the site I will attract freelancers etc that gets payed for each customer he sets up. The service will be a subscription service/ pay for extra service needed. This way with the possibility for subscriber to add his own domain name.

I think the best thing is to develope this service with the existing tools that open source products gives. Also that the company page looks professional very easy for me as admin to delegate work to freelancers and sometimes setting up and design templates for customers.

Can you please give me some views on developing such a service using wordpress, joomla or other good CMS solution. Also a price?
Or does such a service already exist that can be bought?

Kindly regards