Решение типа
if (productPrice > 0) {на
if (productPriceDisplay > 0) {
our_price = formatCurrency(productPrice, currencyFormat, currencySign, currencyBlank);на
our_price = formatCurrency(productPriceDisplay, currencyFormat, currencySign, currencyBlank);
$('#old_price_display').text(formatCurrency(productPriceWithoutReduction, currencyFormat, currencySign, currencyBlank));на
$('#old_price_display').text(formatCurrency(productPriceWithoutReductionDisplay, currencyFormat, currencySign, currencyBlank));просмотрел, так оно и есть productPriceDisplay.