For example
$_producte = Mage::getModel('catalog/product')->load(2974);
echo $_producte->getFinalPrice();
I can get in frontend when insert to .phtml
BUT I can not get final price (with discount) in admin section or in custom product export file.
Price calculation in Magento is a hot mess. You need to load the frontend event area in order to trigger rule calculation (ref Mage_CatalogRule_Model_Observer::processFrontFinalPrice()
configured in Mage_CatalogRule
config.xml).
Mage::app()->loadAreaPart(Mage_Core_Model_App_Area::AREA_FRONTEND,Mage_Core_Model_App_Area::PART_EVENTS);