JSFiddle - React, Tailwind, and code Playground

HTML

<span id="priceToSwap3">$238</span>

<select id="trapsize">
 <option data-price="238">foo</option>
 <option data-price="288">foo</option>
</select>

<select id="trapfabric" >
 <option data-price="0">foo</option>
 <option data-price="20">foo</option>
</select>

JavaScript

$('#trapfabric, #trapsize').on('change', function() {
     var $selected = $('#trapfabric, #trapsize').children(":selected");
     var sum = 0;

     $selected.each(function() {
         sum += $(this).data('price');
     });

     $('#priceToSwap3').html('$' + sum);
});