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.
Though is it not possible to conditionally change the shipping amount based on the selection of quantity but you can add option in your payment question with special pricing to achieve your requirement.
Here are the steps you should follow:
1. Add a standard product in your payment question and add the quantity options:
2. Enable the special pricing by checking the check box and then click next:
3. Set the pricing for every quantity:
The following guides should help you:
Special Pricing: https://www.jotform.com/help/265-What-is-Special-Pricing
Please take a look at the following form and see if this works with you. This is not an ideal solution but is very close to your requirement: http://form.jotformpro.com/form/41560908565965?
Feel free to clone this form for a closer look. The following guide should help you in form cloning: https://www.jotform.com/help/42-How-to-Clone-an-Existing-Form-from-a-URL
Hope this helps.
Do get back to us if you have any questions.