好的，maibe我知道了：

add_filter(\'woocommerce_get_price_html\', \'custom_price\', 10, 2);
function custom_price( $price, $product ) {
  $price = \'from \';
  $price .= \'<del>\' . woocommerce_price($product->regular_price *= 1) . \'</del> \';
  $price .= woocommerce_price($product->regular_price *= 0.9);
    $price .= \' per day\';
  return $price;
}