I\'m developing a script (external to Magento, not a module) which aims to output a text list of all available products, their prices and some other attributes. However, cat
As catalog price rules heavily depend on time, store and visiting customer, you need to set those parameters when you want to retrieve the product final price with it's price rules applied.
So, in your case, make sure that provided product is passed with the desired store and customer group id, which can be set as:
Mage::getModel('catalogrule/rule')->calcProductPriceRule($product->setStoreId('STORE_ID')->setCustomerGroupId('CUSTOMER_GROUP_ID'),$product->getPrice())