The Store module allows you to setup a basic online shop on your site in no time. You can manage stock levels as well as orders. Put your products in multi-level categories (click on any of the sub-categories under the Search bar). The free shop supports Paypal for payment or you can set it so that orders are sent to you via email for payment at a later stage.
Also note that the design of the store module can be changed to suit your web site.