Product Details after checkout!

I m using Hikashop in joomla 1.6.I am having an extra cost on user choice which adds to the product full price. i am succesful in getting user response from a drop down where in user can say yes or no to extra cost. Depending upon that extra cost gets added to real price. but i am stuck now as after checkout(Authorize.net) the product details are displayed i want to add that extra cost there also...I m succesfull in inserting it to order_product table.
please guide where to edit the cost so that in biiling cost that extra cost can be displayed. and
$order_product_total_price =($product->order_product_price+$product->order_product_support)*$product->order_product_quantity;
please ang guide properly as i m new to MVC structure.
thnks

Thanks alot for reply..but creating new custom field only create it in address table....
..(screen shot attched)... where to create custom field in product n cart table...according to suggestion u gave....

but the way i m moving is with out layout override manually have created filed in db product , cart, order table n have changed insert,Update queries accordingly at every step. just stuck in last ..which function of authorize.php is taking values from order table to payement url defined in plugin. sending u next screenshot of the detail page where i want to add extra cost and display it with an extra coloumn there also so that customer knows how much is bieng added to final total. plz help project is on dead line.

here goes screenshot of where i want to display on extra filed which is extra cost. plz guide properly told u im fresh wd cake php structure. n chnges i told you in my earlier msg are breaking cart functionality somewhere wch is i am aware of and will come in testing phase.
thnkx alot

have upgraded to new version...help-> update ...downloaded n installed without uninstalling ealier one. it showed version at the footer 'HikaShop Starter 1.5.1, Joomla!™ Shopping Cart Extension' but cant notice custom filed chnge...is that the right way to upgrade..? thnkx

thkns,
Sorry but order table has my value i somehow found that, and onAfterOrderConfirm function too ...but where only five values are printed...on payement page...
thnks

Hello,
Screen shot for authorize.net in previous post has the product information like description,product name,qty..etc. i want to know that from where this data is going? which is the file....data coming from order table i know but it has lot more fields...how it is sending only these 5 fields...i will add my extra cost there ...as i have it in order table....

it shows no effect if i add my value..tried commenting that code than also it takes data....

Thankx.... added my value to total...again where is this total price in screenshot....either guide to remove it or edit as above...total

Thanks
tried adding static value here...
"x_amount" => round($order->cart->full_total->prices[0]->price_value_with_tax+'10',(int)$currency->currency_locale)

no resluts...my value is here $product->cart_product_support ;

guide how to add it so that is shows in total....have used same to add extra cost in items total..

i am unable to add to calculate it ....either explain where to add or just remove it as total is displayed above no need for it again....plzz
have added in classes/order.php like this

$order->products[$k]->order_product_total_price_no_vat = ($product->order_product_price+$product->order_product_support)*$product->order_product_quantity;
i cn see in cart.php & currenct.php total is calcualting don't know where to add exactly...

how order table is getting values can't find insert query for it..

order_product_support
this field is in order_product
not in order table
will the code u gave will work fine