In WooCommerce, If you want to add custom field in single product page than here is solutions. In this example i was add recommended retail price(RRP). It’s price which manufacturer recommends retailer to sell the product. It will display in any Ads or magazine. Like “RRP : ₹500 ” and main price : ₹ 200
So here is code. Add below line of code in your theme’s functions.php file of your active child theme (or theme) and save the file.


// Add RRP field input at product edit page
add_action( 'woocommerce_product_options_pricing', 'add_RRP_to_products' );
function add_RRP_to_products() {
woocommerce_wp_text_input( array(
'id' => 'rrp',
'class' => 'short wc_input_price',
'label' => __( 'RRP', 'woocommerce' ) . ' (' . get_woocommerce_currency_symbol() . ')',
'data_type' => 'price',
)
);
}
// Save RRP field via custom field
add_action( 'save_post', 'save_RRP' );
function save_RRP( $product_id ) {
if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE )
return;
if ( isset( $_POST['rrp'] ) ) {
if ( is_numeric( $_POST['rrp'] ) )
update_post_meta( $product_id, 'rrp', $_POST['rrp'] );
} else delete_post_meta( $product_id, 'rrp' );
}
// Display RRP field at single product page
add_action( 'woocommerce_single_product_summary', 'display_RRP', 9 );
function display_RRP() {
global $product;
if ( $product->get_type() <> 'variable' && $rrp = get_post_meta( $product->get_id(), 'rrp', true ) ) {
echo '';
_e( 'RRP: ', 'woocommerce' );
echo '' . wc_price( $rrp ) . '';
echo '';
}
}