What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
You can add a flat rate for the shipping by going to payment wizard. If you click next after the products, you will see an option about shipping.
If you click that, "Shipping Cost" options will pops out.
Please refer to this guide: http://www.jotform.com/help/304-How-to-add-shipping-cost-to-Payment-Forms
Hope this helps. Thank you.