Website

I am looking for someone to develop an ecommerce platform quite similar to www.joliebox.co.uk or www.birchbox.com. In fact, my project is so similar, that what I am looking for is to almost replicate their pages with a few differences.

I know they were developed in Magento.

My first question is what platform would you suggest? Only Magento? Or it would also be ok with Wordpress, Joomla, or any other as long as based on an open source platform?

In reference to your answer, how much would you charge to develop a site like this and how much would you charge to stay responsible for its future developing? I am not looking for a one shot task, but rather a kind of partnership to last as long as the project is running. Thank you.