click on your item , look at the top were it says edit , click edit it will take you to the page were you listed you item look towards the bottom it will have a button that says show advanced options click that and above that is a place to write in the shipping cost.
you have to read the descriptions and rules. Sorry but if you dont offer free shipping as you stated then you will get negative feedback and flagged by Listia. PLEASE READ THE RULES.