JSFiddle - React, Tailwind, and code Playground

HTML

<form id="payment-form">
    <label class='control-label'>Plan</label>
    <br>
    <input type='radio' name='Product' value='Pro Monthly' checked>Monthly
    <input type='radio' name='Product' value='Lifetime'>Lifetime</form>Total: <span class='amount'>
        &pound;3 a month
    </span>

JavaScript

$('#payment-form input').on('change', function () {
    var plan = $('input[name=Product]:checked', '#payment-form').val();

    if (plan == "Lifetime") {
        var price = "&pound;30 one-off";

    } else if (plan == "Pro Monthly") {
        var price = "&pound;3 a month";
    }
    $("span.amount").html(price);
});