Thanks to my predecessor Mike Grace for this helpful little script. It extends javascript to add the correct comma places to any number.

Number.prototype.addCommas = function() {
	var nStr = this + ''; // convert number to string
	x = nStr.split('.');
	x1 = x[0];
	x2 = x.length > 1 ? '.' + x[1] : '';
	var rgx = /(\d+)(\d{3})/;
	while (rgx.test(x1)) {
		x1 = x1.replace(rgx, '$1' + ',' + '$2');
	}
	return x1 + x2;
};

Usage:

var item = 250435;
item.addCommas(); //changes number to 250,435