http://support.envato.com/index.php?/Knowledgebase/Article/View/222
Can I offer my items for free on a promotional basis?
Authors may not offer their items for free on the Envato Marketplaces, nor promote free items anywhere on the Marketplaces.
Additionally, if an author is exclusive they may not offer items that are for sale on the Marketplaces for free on another site without voiding their exclusivity agreement with the Envato Marketplaces.