We sell products on ebay UK and our own Zen Cart based website. We currently have a php script run on a cron so that when an an item on the Zen cart database is out of stock, it cancels the relevant ebay items.
In addition, each item has a number which is the number of listings that should be kept active on ebay for that particular item.
The item data is stored in an XML file which is controlled by a Zen Cart module. I believe the project is 80-90% complete and the code is well annotated. I need someone to finish the job off and test it on your own demo systems. There is some redundant code relating to international ebay sites that should be removed. I also need a cache adding to the XML module so that it doesn't refresh every single ebay item each time.
Pm and I'll send you the files to give you an idea of how long it will take so you can price it appropriately.