JSFiddle - React, Tailwind, and code Playground

by spliter

HTML

<ul>
<li>
    <label class="desc main">
        Want to get email ($<span id="price">50</span>/month)
        <input type="checkbox" checked="" id="subscribe" name="subscribe">
    </label>
    Some text
</li>
<li>
    <label class="desc offer">
        -$30 subscribe
        <input type="checkbox"  id="custom_test" name="custom_test">
    </label>
    Please check this to add your own email
</li>
</ul>

CSS

.main {color: green}

JavaScript

var price = document.getElementById('price'),
    origPrice = parseInt(price.innerText),
    reducedPrice = parseInt(price.innerText) - 30;

$('#custom_test').change(function(ev) {
    if (ev.target.checked) {
        price.innerText = reducedPrice;
    } else {
        price.innerText = origPrice;
    }
});