Edit in JSFiddle

function getTimeMoneyStart() {
    
    // set the current date, hours, minutes, and seconds
    var d = new Date();
    var h = d.getHours();
    var m = d.getMinutes();
    var s = d.getSeconds();

    // set the number of hours busy today
    var busy = ($(".busy_hours").val() != "") ? $(".busy_hours").val() : 0;
    
    // calculate the number of free hours today
    var free = 24 - busy;

    // calculate the number of free seconds today
    var left = (free*60*60);

    // convert the number of seconds left to currency!
    var balance = "$" + left.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
    
    $(".balance_start").html("Today's starting balance: " + balance);
}

function getTimeMoneyNow() {
    
    // set the current date, hours, minutes, and seconds
    var d = new Date();
    var h = d.getHours();
    var m = d.getMinutes();
    var s = d.getSeconds();
    
    // set the number of hours busy today
    var busy = ($(".busy_hours").val() != "") ? $(".busy_hours").val() : 0;
    
    // calculate the number of free hours today
    var free = 24 - busy;

    // calculate the number of free seconds left today
    var left = (free*60*60) - (h*60*60) - (m*60) - s;

    // convert the number of seconds left to currency!
    var balance = "$" + left.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
    
    $(".balance_now").html("Today's remaining balance: " + balance);
}

// on page load, show initial balance
getTimeMoneyStart();

// on page load, show balance as if all hours are free
getTimeMoneyNow($("input.busy_hours").val());

$("input.busy_hours").keyup(function(){
    getTimeMoneyStart();
    getTimeMoneyNow();
});

* {
    font-family: Arial, sans-serif;
}

h1 {
    font-size: 1.3em;
    text-decoration: underline;
}

p, input {
    font-size: 1em;
}

p.busy span {
    color: grey;
}

p.balance_now {
    font-weight: 700;
}

input.busy_hours {
    width: 2em;
    text-align: center;
}

hr {
    border: 0;
    border-bottom: 1px solid #eee;
    background: #eee;
}

<h1>Time Is Money Calculator</h1>
<p>Time is money, right? See how much "money" or free time you have left today.</p>

<p class="busy">Hours busy today: 
    <input class="busy_hours" value="0"/> <span>(e.g., 1, .5)</span>
</p>

<hr/>

<p class="balance_start"></p>
<p class="balance_now"></p>