Hi,
When telling about "Web user". Do you mean some manager (editor) of the website or someone having more limited access and can just add products? I’m not sure if you need a multi-merchant system.
In most cases, if your client is a merchant without special IT background, he could simply log in the MODx manager and access the backend of some cart module.
TreasureChest 1.0 to 1.2 backend allows up to two options lists.
In-developement 1.3 version was tested successfully with up to 8 option lists.
TreasureChest’s backend is intuitive.
Priced options are not natively implemented into TreasureChest but this can be programmed if you have some budget. This would be a nice new feature.
By "priced options", I mean options that have an influence on the final price.
Some screenshots of TreasureChest’s backend are available here:
http://modxcms.com/forums/index.php/topic,46813.msg296858.html#msg296858
The options can be set by clicking a product name in the Product Manager.
Unfortunately, I cannot make a screenshot of the page showing options because my site is currently under maintenance. (screenshot was added)
Hope this helps.