Hello Luke,

If I understood you correctly that you want to show a subtotal amount for each row in the cart and already have added a new column in cart table view then the following code might help you to resolve your needs:

 $('.oe_website_sale').on("change", ".oe_cart input.js_quantity", function(event) {
        var $input = $(this);
        var value = parseInt($input.val(), 10);
        var $dom = $(event.target).closest('tr');
        var product_id = parseInt($input.data('product-id'), 10);
        var product_ids = [product_id];
        openerp.jsonRpc("/shop/get_unit_price", 'call', {
            'product_ids': product_ids,
            'add_qty': value
        })
            .then(function(res) {
                var price = res[Object.keys(res)[0]];
                var amount = Number(value * price).toFixed(2);
                var current_subtotal = $dom.find('.amount').text();
                var new_subtotal = current_subtotal.replace(/[\d\.,]+/, amount);
                $dom.find('.amount').text(new_subtotal);
            });
    });

This code requests for the price and multiplies it by the number in qty. field and adds result to .amount element when the quantity is changed (assuming you print initial amount before).

Note: this is only a demonstration code and it only returns unformatted amount. If you would want formatted amount you would need to format it before setting it in .amount element.

UPDATE: modified script to format result and put it into .amount element.