How To Show the Regular Price on Your WooCommerce Cart Page

The add_filter() function registers the woo_show_regular_price_on_cart function to be called whenever the woocommerce_cart_item_price filter is applied.
The woo_show_regular_price_on_cart function takes three parameters: $price, $values, and $cart_item_key.
The $price parameter is the current price of the product in the cart.
The $values parameter contains the cart item data including the product ID, quantity, and other details.
The $cart_item_key parameter is the unique identifier for the cart item.
The function checks if the product is on sale by calling the is_on_sale() method on the product object.
If the product is on sale, the function retrieves the regular price of the product using the get_regular_price() method and formats it using the wc_price() function.
The function then adds the formatted regular price to the cart item’s price using HTML and CSS to strike through the regular price and reduce its opacity.
Finally, the function returns the updated price with the regular price included.