Way to Purchase Product On Website Needs Implementation

We have already built the website and have a nice working CMS built with a MySql database that functions just the way they like. [login to view URL]~devel/wwk2/ We need someone to implement a way for the customer, once they choose the product they want on the site, to be able to purchase it securely. NOTE: WE DO NOT WANT A ZEN OR OSCOMMERCE SOLUTION, we want something to work with what we have set up. We will supply and purchase the merchant account (Paypal Pro), the Private SSL for https. We just need someone to incorporate the last stage of checking out and finishing the transaction (including shipping calculations) and set up the email notifcation to the business and confirmation to the client.