function calculate_cost(id)
{
	var quantityElem = document.getElementById("quantity_" + id);
	if (quantityElem == null)
		return;
		
	var quantity = quantityElem.options[quantityElem.selectedIndex].text;
	
	var priceElem = document.getElementById("price_" + id + "_" + quantity);
	if (priceElem == null)
		return;

	var inputPriceElem = document.getElementById("price_" + id );
	if (inputPriceElem == null)
		return;
		
	inputPriceElem.value = priceElem.innerHTML;
}