JSFiddle - React, Tailwind, and code Playground

HTML

<input type="checkbox" name="item" value="100" class="100" />
<input type="checkbox" name="item" value="200" class="200" />
<input type="checkbox" name="item" value="300" class="300" />

<p>$0.00</p>

JavaScript

$("input[type=checkbox][name=item]").change(function() {
    var amount = 0;
    $("input[type=checkbox]:checked").each(function(){
        amount += parseFloat(this.value,10);
    });
    $("p").html("$"+amount);
});