I'm not so sure this is what the OP had in mind, but I do think it would be nice if instead of buyers sending PMs and organizers manually updating spreadsheets, there was something with a database backend that would allow users access to their own orders. For example, if people could log in, place and/or update their own orders, viewing current pricing and order status in real time, that should make everything easier for everyone. All the organizer would have to do is set up the pricing structure and everything else should take care of itself.
As for billing, I know nothing of PayPal API integration but presumably the billing process could also be automated. That leaves organizers with only having to place the initial order, sort/pack shipments, and mail them.
This can be integrated with the current group buy forum, essentially just replacing the use of Google docs and PMs.