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Display total of configured options

I created this form of checkboxes for a keycap website I am making. I want to use the form to display the sub-total to the customer. I assume I need some form of JS in order to do this but I am completely lost.

I also need this total to be the subtotal of the order when they click the checkout with Paypal button.

On top of that (to save our email from form submits that aren’t orders), I need the form to only submit if the purchase goes through. I am more than happy to go into more detail if you need more explanation but I am utterly lost. I have experience with Java but JS is completely new to me.

Is there any way to get this to work without going to external sources?

Here is my site Read-Only: LINK
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