$[*myTV*]
In your Ditto template use something like this:
$[*myTV*]
<?php $tv = isset($tv) ? $tv : '0'; return number_format($tv, 2) ?>
Grrrr... I should have read your post more carefully.
This might help you: http://wiki.modxcms.com/index.php/PHx/CustomModifiers#phx:price_format