PHP Software to Feed Inventory to Ebay Motors

We are looking for a developer with good Ebay API experience to help with creating a PHP software module for feeding stock inventory from our existing PHP/MySQL database driven truck/van websites into the dealer's respective eBay motors accounts (UK /Ireland). From the dealer's perspective he would want to enter data via his website and then have his stock automatically posted/synched daily to his eBay motors account. We would also be looking to provide the services for future clients and would need to be able to roll out easily and quickly. A dealer would typically have around 50 vehicles for listing. We are open to ideas for the best way of achieving this but presumably Selling Manager Pro/File Exchange CSV would be the way forward. We would be looking at some customisation of our existing back-end (which can be provided) to allow this, or alternatively we can adapt existing files/data to capture any required information for passing through to the software.