jquery if else statements - What am I doing wrong?

Okay so I'm trying to set the value of one form field based on the value of another. Here's the code I have so far, not sure why it isn't working... Gotta love Fridays! lol

var $j = jQuery.noConflict();
var $price = 100;
var $price2 = 75;
var $price3 = 50;
var $price4 = 25;
$j(function () {
    $j( document ).ready(function() {
        $j('.addon-custom-price').val(4); 
    });
    $j('.qty').change(function () {
        var $this = $j(this);
        if ($this.val() > 100 || $this.val() <= 153) {
            $j('.addon-custom-price').val((parseFloat($price4 /$this.val())));
        }
        else if ($this.val() > 70 || $this.val() <= 100) {
            $j('.addon-custom-price').val((parseFloat($price3 /$this.val())));
        }
        else if ($this.val() > 40 || $this.val() <= 70) {
            $j('.addon-custom-price').val((parseFloat($price2 /$this.val())));
        }
        else if ($this.val() > 24 || $this.val() <= 40) {
            $j('.addon-custom-price').val((parseFloat($price /$this.val())));
        }
        else {
            $j('.addon-custom-price').val((parseFloat(0);
        }
    });        
});

Any help would be deeply appreciated :)