document.onkeyup = KeyCheck;       

function KeyCheck(e)
{
   if (document.getElementById("ticketqty")!=null) {
	   	//document.getElementById("price").value=document.getElementById("ticketqty").value;
	  	if (IsNumeric(document.getElementById("ticketqty").value)==true){
			var ticketqty = document.getElementById("ticketqty").value;
			var i=0, counter=0, ticketprice=0;
			for (i=1;i<=ticketqty;i++){
				counter=counter+1;
				if (counter==5) {
					ticketprice=ticketprice+20;
					counter=0;
				}
			}
			ticketprice=ticketprice+(counter*5);
			document.getElementById("showprice").innerHTML="Cost: $"+ticketprice;
			document.getElementById("price").value=ticketprice;
			document.getElementById("product").value="House Brothers Raffle ("+ticketqty+" Tickets)";
		}
   }
}

function IsNumeric(sText)
{
   var ValidChars = "0123456789.";
   var IsNumber=true;
   var Char;
 
   for (i = 0; i < sText.length && IsNumber == true; i++) 
      { 
      Char = sText.charAt(i); 
      if (ValidChars.indexOf(Char) == -1) 
         {
         IsNumber = false;
         }
      }
   return IsNumber;
   }