function UpdateCost() {
  //alert("UpdateCost");
  var sum = 0;
  var sum2 = 0;
  var sl, elem, pr, amt, itm, myProduct, shipping, ship;
  for (i=0; i<10; i++) {
	k=i+1
    sl = 'check_'+k;
    pr = 'amount_'+k;
    itm = 'item'+k;
    amt = 'amount_'+k;
    shipping = 'shipping_'+k;
    elem = document.getElementById(sl);
    ship = document.getElementById(shipping);
    if (elem.checked == true) { 
		sum += Number(elem.value);
		sum2 += Number(ship.value); 
		//alert ("shipping :"  + sum2.toFixed(2));
		myProduct = document.getElementById(itm);
		//alert (itm + " :"  + myProduct.value);
		//document.getElementById(itm).value = myProduct.value;
	}
  }
  document.getElementById('total_amount').value = sum.toFixed(2); }
  //document.getElementById('total_shipping').value = sum2.toFixed(2); }