JSFiddle - React, Tailwind, and code Playground

HTML

<form id="payment" class="nice" method="POST" action="" style="margin-bottom:30px;">    
    <div class="text">
       <p class="amount-text">Your final price is <span class="amount">$0</span></p>
    </div>
    <p class="">
        <input type="checkbox" class="large-check" for="id_chair" name="more" value="500" />Add Chair <span style="font-weight: bold;">$50</span>
    </p>
    <p class="">
        <input type="checkbox" class="large-check" for="id_desk" name="more" value="50" />Add Desk <span style="font-weight: bold;">$50</span>
    </p>
    <button class="btn pay" type="submit">Pay <span class="amount">$0</span></button>
</form>

CSS

button.pay{
    cursor: pointer;
    margin-right: 25px;
    font: 14px/100% Arial, Helvetica, sans-serif;
	padding: .5em 2em .55em;
	text-shadow: 0 1px 1px rgba(0,0,0,.3);
	-webkit-border-radius: .5em; 
	-moz-border-radius: .5em;
	border-radius: .5em;
	-webkit-box-shadow: 0 1px 2px rgba(0,0,0,.2);
	-moz-box-shadow: 0 1px 2px rgba(0,0,0,.2);
	box-shadow: 0 1px 2px rgba(0,0,0,.2);
    color: #fef4e9;
	border: solid 1px #da7c0c;
	background: #f78d1d;
	background: -webkit-gradient(linear, left top, left bottom, from(#faa51a), to(#f47a20));
	background: -moz-linear-gradient(top,  #faa51a,  #f47a20);
	filter:  progid:DXImageTransform.Microsoft.gradient(startColorstr='#faa51a', endColorstr='#f47a20');
}
button.pay:hover {
	background: #f47c20;
	background: -webkit-gradient(linear, left top, left bottom, from(#f88e11), to(#f06015));
	background: -moz-linear-gradient(top,  #f88e11,  #f06015);
	filter:  progid:DXImageTransform.Microsoft.gradient(startColorstr='#f88e11', endColorstr='#f06015');
}

JavaScript

$(':checkbox').change(function(){
    var sum = 1500;
    var names = $(':checked').map(function(){
        sum += (this.value - 0);
        return this.name;
    }).get().join(',');
    var spans = $('span.amount');
    spans[1].innerHTML = sum;
});