Branching Conditional Statements Not Working

I have a prototype where I want to give users the ability to select and unselect add-ons, at their discretion. I have a button instance with True and False values, a base price for the product diamond_base, and want to update that value by 400, depending on if the button is selected. I have tried all manner of things and the closest I’ve gotten is: Button is True and the value is added, the Button is False and no value is removed, Button is True again and the value is added again, but the price never decreases. All this takes place on the Click interaction. What might I be doing incorrectly?

Attached is my branching conditional statements, but this instance changes the button to the selected state and adds the value, without resetting the button or removing the value. Any suggestions are appreciated for a workaround.