Add this text to a plugin file or your theme’s functions file and then change the ’18’ to the id of the category of products you want to apply the filter to.

ID;
$my_product_array = array( 799,796,792 );//add in product IDs
if ( in_array( $product_id, $my_product_array )) {
$textafter = ‘( Upfront Paid in Full Price )’; //add your text
return $price . ‘
‘ . $textafter . ‘‘;
}

else {
return $price;
}
}
add_filter( ‘woocommerce_get_price_html’, ‘themeprefix_custom_price_message’ );