msopOnGetFullCost.php

<?php
/** @var $cost */
/** @var $options */
/** @var $modifications array */
switch ($modx->event->name) {
    case 'msopOnGetFullCost':

        if (!$msoptionsprice = $modx->getService('msoptionsprice')
        ) {
            return false;
        }

        $tkan = isset($options['tkan']) ? $options['tkan'] : 0;
        if (!$tkan) {
            return;
        }

        /** @var  msProduct $product */
        if (!$tkan = $modx->getObject('msProduct', (int)$tkan)) {
            return;
        }
        $optPrice = $tkan->get('price');
        if (!$optPrice) {
            return;
        }
    
        $cost = $cost + $optPrice;
        $cost = $msoptionsprice->formatPrice($cost, true, true);

        $values = $modx->Event->returnedValues;
        $values['cost'] = $cost;
        $modx->event->returnedValues = $values;

        break;

}