I haven't used Squarespace (http://www.squarespace.com/) myself, and don't know the platform well enough to know if it meets your client's needs, but it sounds like what your client wants is pretty close to what Squarespace does. Might be worth looking into.
Have you heard of Spree ? https://github.com/spree/spree
Check out Concrete5 - I haven't used it for a few years, but it worked pretty well for exactly that kind of use case for me a few years back.