If you are making the prints, then you would need a license from the artist to do this--i.e. an agreement saying that you are allowed to make and sell prints. The contract could otherwise say anything the two of you agreed to: it could give you the right to only do one specific print, approved by the artist, in limited quanties, or to sell as many of any kind of print or reproduction of the art as you want. It could set a minimum price you have to charge or not. It could specify that the artist gets a piece of every sale, or simply a flat fee for the grant of the  license. Etc.The best thing to do would be to work with an attorney (either a business lawyer or an intellectual property attorney) to draw up a contract that works for your business model.