Thanks for posting your requirement.
We understand that you want to integrate the payment gateway, please tell us which payment gateway you would like to integrate.
We feel confident that we are the right-fit for your project because we excel in Graphic design, Drupal,Wordpress, PHP/MySQL, PHP5, JavaScript, XML,XHTML/CSS, Joomla.
As a next step, We request you to please initiate the private message board through freelancer so that we can discuss on the requirements and give you a firm cost/timeline.
Best regards,
Dean D Andrea