With Custom Pricing Rules you can add calculated shipping to the total of your form based on the user's answers. To get started, follow these steps:
Add questions to your form which will trigger the custom pricing rule, this includes Price, Products, and Subscription fields. For this example, we will add a $5 shipping charge to all orders under $20.
Go to Configure → Payments → Toggle on the option "Custom Pricing Rules" and click "Add a rule" to add a new custom pricing rule.
Select the question you will use to trigger the custom pricing rule and create a rule to modify the total as required. In this example, a $5 fee is added when the total price is less than 20.
(Optional) Add any other required pricing rules. For example, we might also need to add a 10% tax when the billing country is Australia. To apply the tax to the shipping as well as the price the tax rule should be positioned below the shipping rule.
(Optional) You can also set a label to describe the custom pricing rule in the checkout.
Gotchas
Custom pricing rules are applied in order so if two rules are in effect at the same time the lower one will affect the rules above it.