Looking through the features you ask for, I instantly remebered Avactis. You should check it out, too - it has a pleasant interface And if you already have a site, you can integrate Avactis right into it. You said you know PHP, so you must understand this: when you insert into a page <? NavigationBar(); ?>, it turns to a working one, and this way you can add other parts of the store, too. Very flexible.