I have a possible freelance job in front of me for a distributor who wants product ordering set up but the orders are all P.O.s basically - no actual credit card or paypal transaction. The customer is simply billed and the order archived.

Customers will need to login to this site and each customer will have their own custom catalog of a few dozen products which have been setup via a control panel this distributor uses. So there will be a master catalog of over 1,000 products (perhaps browsable but not to be ordered from on the site) but each customer will only be able to order from the products specified for their accounts.

I know I can build this from scratch but I figured it's worth looking into what ecommerce platforms would get me a nice head start. Obviously shopping cart, order history, catalog management are concepts that I can reuse but are any of the ecommerce systems out there also capable of handling custom catalogs (maybe as multi-stores?) or transactions billed to accounts without credit card? The more I could reuse the better.

I've messed with OSCommerce (way back) and a little Zen Cart more recently. I've also worked on a number of totally custom e-commerce sites. But my knowledge of the open source e-commerce tools is pretty limited and I'm trying to keep the effort as simple as I possibly can on this. I'm pretty flexible on the language of the platform by the way. Thanks in advance.