add_action( 'woocommerce_product_options_pricing', 'custom_woocommerce_product_options_pricing' );

function custom_woocommerce_product_options_pricing() {
    $price_index = '_custom_price';

    woocommerce_wp_text_input(
        array(
            'id' => $price_index,
            'value' => get_post_meta( get_the_ID(), $price_index, true ),
            'data_type' => 'price',
            'label' => __( 'Custom price', 'woocommerce' ) . ' (' . get_woocommerce_currency_symbol() . ')'
        )
    );
}

add_action( 'woocommerce_admin_process_product_object', 'custom_woocommerce_admin_process_product_object', 10, 1 );

function custom_woocommerce_admin_process_product_object( $product ) {
    $price_index = '_custom_price';

    $price = wc_clean( wp_unslash( $_POST[ $price_index ] ) );

    update_post_meta( $product->get_id(), $price_index, $price );
}

$price_index = '_custom_price';

    echo wc_price( get_post_meta( get_the_ID(), $price_index, true  ) );