public virtual PriceInfo Substract( 
   IWithPrice priceholder 
)

class MyPage : System.Web.UI.Page
{
    private void RenderOrderLine(Dynamicweb.eCommerce.Orders.OrderLine orderLine, Dynamicweb.Rendering.Template template)
    {
        Dynamicweb.eCommerce.International.Currency temporaryContextCurrency = Dynamicweb.eCommerce.Common.Context.Currency;
        if (orderLine.Price.Currency != null)
        {
            Dynamicweb.eCommerce.Common.Context.Currency = orderLine.Price.Currency;
        }
        Dynamicweb.eCommerce.Prices.IWithPrice totalDiscountPriceInfo = (Dynamicweb.eCommerce.Prices.IWithPrice)orderLine.Product.Discounts.TotalDiscount.Multiply(orderLine.Quantity);
        totalDiscountPriceInfo.Price.Currency = Dynamicweb.eCommerce.Common.Context.Currency;
        Dynamicweb.eCommerce.Prices.PriceInfo netPrice = orderLine.Price.Substract(totalDiscountPriceInfo);
        RenderPriceInfo(netPrice, template, "Ecom:Order:OrderLine.TotalPriceWithProductDiscounts");
        Dynamicweb.eCommerce.Common.Context.Currency = temporaryContextCurrency;
    }

    public static void RenderPriceInfo(Dynamicweb.eCommerce.Prices.IPriceInfo price, Dynamicweb.Rendering.Template template, string tagName)
    {
        if (template.HtmlHasPartialTag(tagName))
        {
            if (template.TagExists(tagName + ""))
            {
                template.SetTag(tagName + "", price.PriceFormatted);
            }
            if (template.TagExists(tagName + ".Price"))
            {
                template.SetTag(tagName + ".Price", price.PriceFormattedNoSymbol);
            }
            if (template.TagExists(tagName + ".PricePIP"))
            {
                template.SetTag(tagName + ".PricePIP", price.PricePIP);
            }
            if (template.TagExists(tagName + ".PriceFormatted"))
            {
                template.SetTag(tagName + ".PriceFormatted", price.PriceFormatted);
            }
            if (template.TagExists(tagName + ".PriceWithVAT"))
            {
                template.SetTag(tagName + ".PriceWithVAT", price.PriceWithVATFormattedNoSymbol);
            }
            if (template.TagExists(tagName + ".PriceWithVATFormatted"))
            {
                template.SetTag(tagName + ".PriceWithVATFormatted", price.PriceWithVATFormatted);
            }
            if (template.TagExists(tagName + ".PriceWithoutVAT"))
            {
                template.SetTag(tagName + ".PriceWithoutVAT", price.PriceWithoutVATFormattedNoSymbol);
            }
            if (template.TagExists(tagName + ".PriceWithoutVATFormatted"))
            {
                template.SetTag(tagName + ".PriceWithoutVATFormatted", price.PriceWithoutVATFormatted);
            }
            if (template.TagExists(tagName + ".VAT"))
            {
                template.SetTag(tagName + ".VAT", price.VATFormattedNoSymbol);
            }
            if (template.TagExists(tagName + ".VATFormatted"))
            {
                template.SetTag(tagName + ".VATFormatted", price.VATFormatted);
            }
            if (template.TagExists(tagName + ".VATPercent"))
            {
                template.SetTag(tagName + ".VATPercent", price.VATPercent);
            }
            if (template.TagExists(tagName + ".VATPercentFormatted"))
            {
                template.SetTag(tagName + ".VATPercentFormatted", price.VATPercentFormatted);
            }
            bool isZero = price.Price == 0;
            template.SetTag(string.Format("{0}.IsZero", tagName), Base.IIf(ref isZero, "true", ""));
        }
    }
}