WooCommerce Before Cart

woocommerce_before_cart.php

<?php

add_action( 'woocommerce_before_calculate_totals', 'add_custom_price' );
function add_custom_price( $cart_object ) {
    $custom_price = 0; // This will be your custome price  
    //Your Custom Price Forumula goes here
    $totalWeight = 50; // you can this variable value from post/get or cookie etc. 
    $unitWeight = 8; //8lbs default unit for basic unit price;
    $unitPricePerWeight = (float) 0.44; //your unit price per 8lbs weight; 
    $noOfOrderDays = 10; // you can populate this varaible value from post/get/cookie or session. 
    $custom_price = (float) ($totalWeight/$unitWeight) * $unitPricePerWeight * $noOfOrderDays;
    $target_product_id = 12 // you conditional product ID
    foreach ( $cart_object->cart_contents as $key => $value ) {
        if ( $value['product_id'] == $target_product_id ) {
            $value['data']->price = $custom_price;
        }        
        //$value['data']->price = $custom_price;
    }
}