vadenko

add_filter( 'woocommerce_get_price_html', 'product_price_free_zero_empty', 100, 2 );

function product_price_free_zero_empty( $price, $product ){
if ( '' === $product->get_price() || 0 == $product->get_price() ) {
    $price = '<span class="woocommerce-Price-amount amount">Цену уточняйте</span>';
}
return $price;
}