add_filter( 'wdp_save_cart_item_keys', function ( $keys ) {
  $keys[] = 'booking';
  return $keys;
}, 10, 1 );

add_filter( "wdp_get_product_price", function ( $price, $product, $price_mode, $item_meta ) {
  if ( isset( $item_meta['booking']['_cost'] ) ) {
    $price = $item_meta['booking']['_cost'];
  }
  return $price;
}, 10, 4 );