Add a default meta_value to new posts

Add this to your functions.php in your template folder.

<?php

//Set Default Meta Value
function set_default_meta_new_post($post_ID){
$current_field_value = get_post_meta($post_ID,'YOURMETAKEY',true); //change YOUMETAKEY to a default 
$default_meta="100"; //set default value

if ($current_field_value == '' && !wp_is_post_revision($post_ID)){
    add_post_meta($post_ID,'YOURMETAKEY',$default_meta,true);
}
return $post_ID;
}

add_action('wp_insert_post','set_default_meta_new_post');

?>