JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
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You can try the method described in this guide or as an alternative, you can use form collapse fields and add checkbox fields for the options:
Now you can add the price of each item as a calculation value:
Finally you can add a form calculation widget, that will calculate the total of the order:
On the payment field you should now select the "collect donations" option > get amount from the "calculation field":
You can test and clone the demo form:
Let us know if we can assist you further.