wordpress Invoice plugin development or customization of existing multisite plugins to integrate a billing system with recurring paypal payments into GeoTheme child theme

REQUEST: wordpress Invoice plugin development or customization of existing multisite plugins to integrate a billing system with recurring paypal payments into GeoTheme child theme Skills requested: Professional experience in coding and developing of WP wordpress, WPMU Multisite, PHP, MySQL Database, HTML, CSS, Jquery, Plugin & Theme developments, etc. You need to work independent, conscientious and intuitive to enable an easy to use plugin. Situation: Using a GeoTheme child theme within a multisite wordpress installation, users are able to purchase price packages (daily or monthly basis depends on setup) for advertisements of their businesses. The GT developer of the theme provides NO billing system within the purchase process. Only the transaction of the purchase and for recurring payments only paypal payments will be transferred for purchase within the GeoTheme system settings. Now an easy to use billing & reporting system needs to be created, enabled and integrated into the system or payment process. Development request: there are two possible ways which could be used to go further 1. develop a new plugin or 2. use existing plugin and customize for unique and own needs with the core functionalities stated below. The fastest and cheapest way is preferred. All rights and developing details as well notes for creation on this will be transferred to the ordering client (me). After finalize the (from you created development) plugin, this wordpress addon of the GeoTheme theme and will be sold later on at [login to view URL] Find here more details (starting at page 2) by clicking this URL: [login to view URL] Please refer to this inquiry as soon as possible, if you are able to help & provide me with your offer and time schedule. With my best regards, Alex