hook_form_alter

Hello,

I've doing a module which call a hook_form_alter in a hook_nodeapi.

I'd like to pass a variable in my hook_form_alter to get it in my hook_form_alter, how can I do it?

<?php
function maj_attributs_nodeapi(&$node, $op){
	
//my tests

// I get a var from the database : $prix_revendeur

	if(isset($prix_revendeur)){
		drupal_set_message(t('Prix %prix_revendeur .', array('%prix_revendeur' => $prix_revendeur)));
			

		function maj_attributs_form_alter(&$form, $form_state, $form_id) {
			if($form_id=='product_node_form'){
                               // if I do this I have nothing in my field
				$form['base']['prices']['reseller_price']['#default_value']=$prix_revendeur;

                             //but with the code below it works
			    $form['base']['prices']['reseller_price']['#default_value']='12';

   
                          // how can I get the $prix_revendeur var in my hook_form_alter?
			}
		
		}
		
		
	}
		
}

?>

Thanks in advance for your help