Hi,
We can do this for you.
However, we would strongly recommend that you continue with Joomla. We are sure your decision to move away from Joomla must be driven by some issues that you are facing. Trust us, Joomla is very very robust, and the latest versions have very strong security too. If it is true that your decision to move away is because of issues you are facing, we could sort all those issues out instead, and redo your site on the latest version of Joomla with a fully responsive template.
Alternatively, as you have sought, we can do the site using PHP natively.
We are open and available for any discussion.
Regards