How to intercept the loading of a field?
Ok, i figured it out.  I put this code into my template.php of my theme:

function johncustom_field__field_price(&amp;$variables) {
        if($variables['element'][0] == '$0.00') return 'Free';
        else return $variables['element'][0];
}


I also had to clear the cache several times before this function would fire.