JSFiddle - React, Tailwind, and code Playground

HTML

<form name="config" id="config">
    <div class="row-fluid">
         <h3>Memory</h3>

        <input type="radio" name="section1" value="4gb" onclick="changePrice(1,0)" checked="checked" />4gb
        <br/>
        <input type="radio" name="section1" value="8gb" onclick="changePrice(1,100)" />8gb (+$100)
        <br/>
        <input type="radio" name="section1" value="16gb" onclick="changePrice(1,200)" />16gb (+$200)
    </div>
    <div class="row-fluid">
         <h3>Primary Hard Drive</h3>

        <input type="radio" name="section2" value="dell" onclick="changePrice(2,0)" checked="checked" />Dell
        <br/>
        <input type="radio" name="section2" value="asus" onclick="changePrice(2,100)" />Asus(+$100)
    </div>
</form>
<div id="price"></div>

JavaScript

var displayPrice = document.getElementById("price");
var baseNum = 200;
displayPrice.innerHTML = baseNum;
var sections = {};

function changePrice(section, val) {
    // add or update the section value
    sections[section] = val;
    // start with the base price
    var sum = baseNum;
    // loop over all the sections and add them to the base price
    for (var key in sections) {
        sum = sections[key] + sum;
    }
    displayPrice.innerHTML = sum;
}