I want to add up the cost of various options, and generate a total on the form

PayPal creates a form that allows a choice of items, and generates a total.  How can I do the same kind of thing on Jotform for folk who want to pay by check?

You can use regular checkbox or radio button field to create a product options and use the form calculation widget to get its total.

Here's how to perform calculation on form: https://www.jotform.com/help/259-How-to-perform-calculation-in-the-form

So basically, you need to have a dropdown or radio button that asks the user of the payment method. When the user picks check payment, you can simply show fields that is relevant to check payments like the regular checkbox field (products) and the total calculation field.

Here's how to create show/hide condition in your form.

If you need further assistance, let us know.