JSFiddle - React, Tailwind, and code Playground

HTML

<table>
<td width="343">Package*</td>

        <td colspan="4">

        <select class="purple" name="package">

            <option value="standard">Standard - &euro;55 Monthly</option>

            <option value="premium" selected="selected">Premium - &euro;99 Monthly</option>

            <option value="platinum">Platinum - &euro;149 Monthly</option>

        </select>

        </td>

        <tr>

        <td width="343">Would You like to avail of our multiyear discounts?*

        <br />See <a href="#dialog" name="modal">Pricing</a> for more details

        </td>

<td colspan="4">
    <input name="discount" type="radio" id="Yes" value="Yes" />Yes
    <input name="discount" type="radio" id="No" value="No" checked="checked" />No<br />  
    <select class="purple" name="discountselection" id="discountselection">
        <option value="1" selected="selected">1 Year</option>
        <option value="2">2 Years</option>
        <option value="3">3 Years</option>
    </select> 
    <input name="costlabel" type="label" id="costlabel" />
</td>
</table>

JavaScript

$('#discountselection').hide();
$('#costlabel').hide();

$('#No').click(function() {
    $('#discountselection').hide();
    $('#costlabel').hide();
});

$('#Yes').click(function() {
    $('#discountselection').show();
    $('#costlabel').show();
});



$("#discountselection").change(function()  { 
    var
        selected_value = $("#discountselection").val(),
        discount = [12, 24, 36],
        package = $("select[name=package]").val(),
        package_prices = {'standard': 45, 'premium': 85, 'platinum': 134 },
        cost = package_prices[package] * discount[selected_value-1];
console.log(package);
console.log(discount[selected_value-1]);
    $("#costlabel").val(cost);
});