JSFiddle - React, Tailwind, and code Playground

HTML

<select id="country">
    <option value=17>Option 1</option>
    <option value=18>Option 2</option>
    <option value=19>Option 3</option>
</select>

<p id=goods>£5.00</p>

<p id=shipping>£0.00<p>
    
<p id=full_price>£5.00</p>

JavaScript

$("#country").change(function() {
        var shipping_cost = parseFloat($("#shipping").text().replace(pattern, ''));
        var total      = parseFloat($("#goods").text().replace(pattern, ''));
        var pattern = /[^0-9.-]+/g;
        var result = total + shipping_cost;
        console.log(result);

           if($(this).val() == "17") {
               $("#shipping").text("£0.00");
               $("#full_price").text("£"+result);
           } else {
               $("#shipping").text("£5.00");
               $("#full_price").text("£"+result);
           }
    });