Secure PayPal Invoicing Application

I need an application written which essentially mimics the Paypal invoicing page, without having any other access to Paypal. The purpose of this is to allow staff of my company to send and share links to Paypal invoices, as well as verify whether or not they have been paid, without giving access to the Paypal account as a whole. The application will be hosted on our own LAN server and therefore while basic security practices are obviously important, it does not have to be security hardened to the extent that it would be if it was hosted on a public webserver. I anticipate that this would be a relatively quick and hopefully simple project for the right developer - however experience with the Paypal API is of course a must. Due to the importance of this obviously sensitive information, I will only be accepting Freelancers with a high rating and a good amount of experience.