Create a plugin for that. So you need to create new module Or add following code into your existing module.
SR/StackExchange/etc/adminhtml/di.xml
<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
<type name="Magento\Catalog\Model\Config\Source\Product\Options\Price">
<plugin name="sr_stackexchange_add_price_type" type="SR\StackExchange\Plugin\Catalog\Model\Config\Source\Product\Options\Price" sortOrder="1"/>
</type>
</config>
SR/StackExchange/Plugin/Catalog/Model/Config/Source/Product/Options/Price.php
namespace SR\StackExchange\Plugin\Catalog\Model\Config\Source\Product\Options;
class Price
{
/**
* {@inheritdoc}
*
* @codeCoverageIgnore
*/
public function afterToOptionArray(
\Magento\Catalog\Model\Config\Source\Product\Options\Price $subject,
array $priceTypeOption
){
$priceTypeOption[] = ['value' => 'new_type', 'label' => __('New Type')];
return $priceTypeOption;
}
}
Clear magento cache.