Real-time action in C# .NET

A simple real-time auction where users can bid on an offered product(no database link needed, just mock data). 20 users can participate at the same time in the auction(20 clients, its enough if i can run it in localhost). They can only offer within a given time(example > auction continues for 1 hour, and every time someone offers time extends with 2 minutes). The user interface is not important, it can be a very simple html page. The most important aspect is that it has to be real-time, so the users can see each others offer and the remaining time.