JSFiddle - React, Tailwind, and code Playground

HTML

<select name="treatment[]" class="col-sm-12 country" id="" multiple="multiple">
    <option value="fish" data-price="200">Fish</option>
    <option value="chicken" data-price="500">Chicken</option>
</select>
<input type="text" id="total" />

JavaScript

$('.country').click(function () {
    var price = 0;
    $('option:selected', $(this)).each(function () {
        console.log($(this).data('price'));
        price += $(this).data('price');
    });
    $('#total').val(price);
});