Billing/delivery cost calculator and payment integration

We are looking for a very capable PHP/Ajax coder to implement integrate an online payment gateway to and already existing site to enable online payment. On this same site. We want to add a new function, a delivery cost calculator to enable registered and non registered customers to find our delivery cost of orders they wish to make. There will be need to include AJAX function to refresh cost should additional items be added to the delivery cost calculator. There are certain rules/constants (to be provided) that will be used by the calculator to workout the delivery cost. These figures will be changeble by admin We are particularly looking for an experienced and competent PHP developer who has implemented e-commerce websites. Bidders MUST show previous similar work to demonstrate capability inorder to be considered for this project. Regards