Level of difficulty to recreate the Lightstreamer server and the three client parts?

I need to create a bi-directional communication with a javascript application and desktop applications for inputting text and binary data to and from the server.

Lightstreamer is awesome, but I need some paid features that are on the expensive side (20 thousand euros and above).

So I buy or build it .....

Source parts:

In my case, I will start / write a server on Win2012 / IIS-8 / .NET4.5x Clients: .NET, Mono, Javascript

At first glance, it seems that an experienced developer could build such a thing in about a week.

Is this fair or is there magic in the light stream, which would be very difficult?