Refresh ASP.NET page periodically to display real time data from SQL Server

[ezasabc]

I have a shopping cart based application in asp.net 2.0 which uses the concept of group buying.My requirement is that when user checks out a particular product,he should do it with the latest price of that item at that time.Now there is a scenario.I have a product with price 50.I did a checkout.50 is displayed in my cart.At the same time some other user is accessing the product and now based on some business logic,we calculate the price.the second user did some activity which reduced the price to 45. I have a trigger which updates all shopping cart items with this new price.I want to show this updated price on the frontend of the first user without a postback. or i want to give him a message that this price has changed so do a page refresh.I have the following options.1) The repeater control which shows the cart should be put under an update panel and that update panel should be refreshed after some interval using a timer.2) use SQL Server notification services and invalidate the cache as soon as the data changes in database.I do not want to use notification services as I am not caching the data.Secondly problem with update panel and timer control in that it will be a overhead to refresh it and refresh time is hard to find.Please tell me a way to accomplish this scenario.