Using PHP to get megabytes:
<?php
$postid = get_queried_object_id();
echo round(filesize($GLOBALS[‘currSS’]->ss_media_dir.ss_get_post_meta($postid, ‘ss_media_filename’, true))/1000000);
?>
Just put that anywhere on the product page where you want the megabytes to show up. If you want KB, change the 1000000 to 1000.
Give that a go and let me know