Add Total Price Calculation to your WooCommerce Product Page with AJAX https://alexanderdejong.com/wordpress/wp-tutorial/add-total-price-calculation-woocommerce-product-page-ajax/

content-single-product.php

add_action( 'woocommerce_single_product_summary', 'woocommerce_total_product_price', 25 );
function woocommerce_total_product_price() {
    global $woocommerce, $product;
    // let's setup our divs
    echo sprintf('<div id="product_total_price" style="font-size: 16px; font-weight: 200;">%s %s</div>',__('Total Price (incl Tax):','woocommerce'),'<span class="price">'. get_woocommerce_currency_symbol() .' ' .$product->get_price().'</span>');
    ?>
        <script>
            jQuery(function($){
                var price = <?php echo $product->get_price(); ?>,
                    currency = '<?php echo get_woocommerce_currency_symbol(); ?>';

                $('[name=quantity]').change(function(){
                    if (!(this.value < 1)) {

                        var product_total = parseFloat(price * this.value);

                        $('#product_total_price .price').html( currency + product_total.toFixed(0));

                    }
                });
            });
        </script>
    <?php
}

how to add decimal? Example: 2,00