Numeric Range Validation PLEASE HELP ASAP

I am trying to update the code you see below with Numeric Validtion. This is a function that is called to verify a numeric field. But for my life I cant figure it out. I have attached the code below. All I am trying to do is update the code to allow a numeric range from 0 - 35000.. But still have the function do what it is already doing. Please help ASAP, I have to get this working by this afternoon. PLEASE HELP.. THANKS GUYS!

 function DrawNumericValidation(source, args){
	var tb = source.id.split("-")[0];
	var txt = document.getElementById(tb).value;
	txt = txt.replace(/ /g,"");
	document.getElementById(tb).value = txt;

	args.IsValid = true;

	if (txt == null  ||  txt.length == 0) {
		args.IsValid = true;
	}
	else {	
		for (var i = 0; i < txt.length; i++) {
			var c = txt.charCodeAt(i);
			if ((c < 48 || c > 57)  &&  c != 46) {
				args.IsValid = false;
			}
		}
	} 

Code (markup):