Массово: применить наценку ко всем товарам каталога с пересчетом от базовой.

AddEventHandler("iblock", "OnBeforeIBlockElementAdd", Array("MyClassPrice", "OnBeforeIBlockElementAddHandler"));
class MyClassPrice
{
    function OnBeforeIBlockElementAddHandler(&$arFields)
    {
        Cmodule::IncludeModule('iblock');
        Cmodule::IncludeModule('catalog');

        $IBLOCK_ID = 5; // Инфоблок
        $EXTRA_ID = "1"; // Наценка
        $PRICE_ID = "4"; // Тип цены

        $getElementId = CIBlockElement::GetList(
            Array("ID" => "ASC"),
            Array("IBLOCK_ID" => $IBLOCK_ID),
            false, false,
            Array('ID',)
        );
        while ($arID = $getElementId->Fetch()) {
            $arFields = Array(
                "PRODUCT_ID" => $arID['ID'],
                "CATALOG_GROUP_ID" => $PRICE_ID,
                "EXTRA_ID" => $EXTRA_ID,
                "CURRENCY" => "RUB",
            );
            $res = CPrice::GetList(
                array(),
                array(
                    "PRODUCT_ID" => $PRODUCT_ID,
                    "CATALOG_GROUP_ID" => $PRICE_TYPE_ID
                )
            );
            if ($arr = $res->Fetch()) {
                CPrice::Update($arFields);
            } else {
                CPrice::Add($arFields);
            }
        }
    }
}