WooCommerce Price Overriding in Cart Dynamically - wordpress

Question

Let me explain clearly i have created one table in database with columns( bed_type, dimensions*thickness, price, ).refer image by default single is selected with dimension and thickness as shown in image now user can select select any bed type,dimension and thickness so according to that price will change I am sending ajax request to database if condition matched then i am getting price in this paragraph
<p class='prices' id='demo' style='margin-left:22%;'></p>
now i want to pass the calculated price in cart how can i achieve this. I am trying this task from last week but not getting any result. please guide me
Ajax for Bed Type
function price()
{
var current_id=this.id;
var dimension = document.getElementById(current_id).value; // dimension
var thickness = document.getElementById("thickness").value;
var res = dimension.concat('x'+thickness);
jQuery.ajax({
url: "/Mattressbox/price",
data: {price: res},
type: "POST",
success:function(data){
$("#result").html(data);
},
error:function (){}
});
}
price.php code
global $wpdb;
if(isset($_POST['price']))
{
$price_value = $_POST["price"];
$result = $wpdb->prepare("SELECT price FROM wp_single WHERE size='".$price_value ."'",$id,null);
$row = $wpdb->get_row($result);
$price = $row->price;
if($price > 0)
{
echo '<script>';
echo 'var name = ' . json_encode($price) . ';';
echo 'document.getElementById("demo").innerHTML ="₨ " + name;';
echo '</script>';
}
else
{
//echo "failed";
}
}
in this paragraph i am getting dynamic price using ajax
<p class='prices' id='demo' style='margin-left:22%;'></p>
now i am trying to pass this paragraph in place of custom price like this
add_action( 'woocommerce_before_calculate_totals', 'add_custom_price' );
function add_custom_price( $cart_object ) {
$custom_price = "<p class='prices' id='demo' style='margin-left:22%;'></p>"; // This will be your custom price
foreach ( $cart_object->cart_contents as $key => $value ) {
$value['data']->price = $custom;
}
}
only static price is going in cart but this is not working please suggest something...thank you..