JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" disabled id="eventprice" name="eventprice" class="form-input" />
<select id="select">
    <option data-cost="5">Event 1</option>
    <option data-cost="10">Event 2</option>
</select>

JavaScript

$('#select').change(function () {
      var str = $(this).find('option:selected').data('cost');
      $('#eventprice').val(str);
  });

  // $('#select').trigger('change');