Although in theory, it’s possible to create an e-commerce web site for free, in real life, this is not possible.
2 kinds of solutions to create an e-commerce web site
You can either use an Open Source CMS or use a SAS application.
Open Source CMS
You can use an Open Source software to manage your e-commerce web site. The software will not cost you anything, but you will likely need the assistance of expert to install and configure the software. Keep in mind there are extra costs : you will need a server (preferably hosted to make sure it’s realiable), and then you might to pay to get a nice theme and plugins for extra functions. Also you will need to pay for payment solutions.
The recommended solution is WordPress+WooCommerce. We use to recommend PrestaShop, but we, now think that WooCommerce is a much interesting solution.
Magento is too dificult to install for a shop that is not huge. The other solutions (OpenCart, OsCommerce, ZenCart) are not interesting.
These solutions provides you an easy way to your inline shop. They provide your e-commerce web site as a service and you will need to pay a monthly fee. They provide you with an integrated solution: every thing is included (payments, hosting …) nothing more to pay and to configure. But you can only do what’s defined in their solution.
To read the list of solutions and their prices head to the French version of this article.