Richard,
Spotted your entry and though I don’t have a specific answer (nor do I know of anything out there custom-made like what you’re wanting), I might be able to point you in the right direction.
Someone who could help you with this is Jae Barclay over at http://www.creat-ee.com. He does all kinds of webinars and custom courses on extending the usability of EE. I’ve taken a webinar from him, and this is the very sort of thing he’s discussed, in terms of taking EE (along with modules/extensions like BrilliantRetail and DataGrab) and creating the sort of custom solution you’re needing.
He’s very knowledgeable and could certainly help point you in the right direction. My gut tells me that the key to creating what you need is combining the right extensions/modules and planning it out to get exactly what you want, as this seems like a fairly custom solution. That’s likely why you’re not finding something out-of -the-box that can do this sort of thing.
Best of luck,
Andy