Level of difficulty to recreate Lightstreamer Serv

Question

I need to build bidirectional communication to a javascript app and to desktop apps for text and binary data going to and from a server.

Lightstreamer is awesome, but I would need some of the paid features, which are on the expensive side (20K Euro and up).

So do I buy it or build it.....

Baseline pieces:

In my case, I would be running/writing server on Win2012/IIS-8/.NET4.5x Clients: .NET, Mono, Javascript

On the surface, it appears an experienced developer could build such a thing in about a week.

Is that fair, or is there magic in lightstreamer that would be very difficulty?