This is my first time being asked to do the backend work for a simple shopping site: php/mysql catalog, users, orders, etc. The site already has the basic front-end design done, including basic html/css.
What would be a reasonable fee for mostly just the backend for the shopping site?
It depends a lot on what platform you are using. There's not one answer. A simple project like this can get complicated fast.
A custom eCommerce back-end – 50K +
Using a open source CMS such as; Magento 5 – 15K depending on customizations.
Again, very rough but still I would say that is a good ball park.