adding online store to existing my wordpress website

Already have a simple website([login to view URL]) for my henna needs on word press along with [login to view URL] job is to add 20 to 25 products as a online store to the existing website.I have all products information ready with me what exactly I am looking are below features. Need a online store for all products which can be integrated to my wordpress website and should be free. The shopping cart should be able to edit the price settings like single item say $2,if 2 price should be $1 etc. I have all the products ready with needed information and images need to be formatted in the store USPS shipping feature need to be integrated in the shopping cart I need the online store with above features free source. pls ping me if u have any questions before u bid for the project. I know this is very simple work as I dont have time for myself posting it here. The max bid is $30 I ignore for other bidders.