Custom PHP work on existing site

General information for the website: This is an ecommerce site selling window coverings
Kind of development: Customization of existing website
Description of requirements/features: Work is to be done on an existing php custom site , this site has been up and running and we are now going thru doing some changes to layout , php and shopping cart.

The work required for this site will be ongoing as we have now been given approval from our company to see how much work we can generate from the site

The address is http://bit.ly/1QEB8oB

1. Shopping Cart to be altered slightly with new item additions
2. Layout slightly changed
3. We also need to update reporting and additional items within the site
Extra notes: I am ideally looking for someone that can provide ongoing work and has a very good knowledge of php and ecommerce sites